remove the legacy screenshot applet from source

It'd be nice to remove the legacy screenshot applet before 6.3 is cut.

When this happens we also need to remove the code from the newer screenshot plugin that enables the legacy applet when the newer plugin is uninstalled, since this code will no longer make sense.

Testing notes

1. CI plans are deleted.
2. Ensure nothing is using the these property keys: (including documentation)
   1. jira.screenshotapplet.enabled
      • ✔︎ not in jira
      • ✔︎ not in jira-html5-attach-images
      • ✔︎ referenced in https://confluence.atlassian.com/pages/viewpage.action?pageId=296092170, notified wthompson that the page should be removed
   2. jira.screenshotapplet.linux.enabled
      • ✔︎ not in jira
      • ✔︎ not in jira-html5-attach-images
   3. jira.screenshotapplet.signscreenshotapplet (used to enable the maven profile)
      • ✔︎ still used in jira-html5-attach-images to activate the profile
      • ✔︎ removed from jira's bin/builds/deploy-jira-project.sh
      • ✔︎ removed from jira's jdk8 plan template
   4. atlassian.keystore.storepass (used in maven)
      • ✔︎ removed from deploy-jira-project.sh
      • ✔︎ removed from jira's jdk8 plan template
3. Deprecate:
   1. APKeys.JIRA_SCREENSHOTAPPLET_ENABLED
      • ✔︎ added @deprecated
      • ✔︎ not used in jira-html5-attach-images
      • nuke on 7.0-breakit
   2. APKeys.JIRA_SCREENSHOTAPPLET_LINUX_ENABLED
      • ✔︎ added @deprecated
      • ✔︎ not used in jira-html5-attach-images
      • nuke on 7.0-breakit
4. Remove unused i18n keys, make sure they're really unused. (check jira-html5-attach-images)
   1. attachfile.paste.label
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   2. attachfile.filename.label
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   3. attachfile.applet.filename.error
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   4. attachfile.comment.update.label
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   5. attachfile.applet.configuration.error
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   6. attachfile.applet.security.problem
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   7. attachscreenshot.description.line1
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   8. attachscreenshot.description.line2
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   9. webfragments.view.issue.opsbar.operations.attachments.screenshot
      • ✔︎ removed
      • ✔︎ not used in jira
      • ✔︎ not used in jira-html5-attach-images
   10. attachscreenshot.title
       • jira-html5-attach-images was using it from JIRA, the key has been moved to jira-html5-attach-plugins as attach.screenshot.title
   11. admin.issue.operations.plugin.attach.screenshot.name
       • ✔︎ removed
       • ✔︎ not used in jira
       • ✔︎ not used in jira-html5-attach-images
   12. attachment.service.error.screenshot.applet.disabled
       • ✔︎ removed
       • ✔︎ not used in jira
       • ✔︎ not used in jira-html5-attach-images
   13. attachment.service.error.screenshot.applet.unsupported.os
       • ✔︎ removed
       • ✔︎ not used in jira
       • ✔︎ not used in jira-html5-attach-images
5. Ensure removal of properties from jira-core/src/main/resources/jpm.xml isn't problematic.
   1. jira.screenshotapplet.enabled
      • ✔︎ left as-is
      • I think it'll be problematic, given it'll change the behaviour of the isScreenshotAppletEnabled() API, so I'll leave them around till those APIs are nuked. (nuke on 7.0-breakit)
   2. jira.screenshotapplet.linux.enabled
      • I think it'll be problematic, given it'll change the behaviour of the isScreenshotAppletEnabled() API, so I'll leave them around till those APIs are nuked. (nuke on 7.0-breakit)
6. Ensure jira-webapp/src/main/gmaven/createIdeaArtifact.groovy continues to work
7. Ensure no static URLs to /secure/applet/screenshot.jar
   1. Deleted com.atlassian.jira.webtests.ztests.screenshot.TestScreenshotApplet
8. Ensure nothing's using:
   1. secure/popups/attachscreenshot.jsp
   2. /includes/deployJava.js
9. Ensure these help paths aren't used:
   1. screenshotapplet.url=Attaching+a+Screenshot
   2. screenshotapplet.title=Attaching a Screenshot
   3. working_with_issues.screenshotapplet.url=Attaching+a+Screenshot
   4. working_with_issues.screenshotapplet.title=Attaching a Screenshot
10. Check if com.atlassian.jira.web.action.issue.AttachScreenshot is used anywhere (perhaps it's used in the jira-html5-attach-images).
11. Remove code from jira-html5-attach-images that disables/enables the JIRA plugin. (release + bump in JIRA)
12. Check if com.atlassian.jira.plugin.webfragment.conditions.CanAttachScreenshotToIssueCondition is used anywhere.
13. Remove anything using the #attach-screenshot HTML ID (e.g. CSS, JavaScript, etc)
14. Remove com.atlassian.jira.web.action.issue.ManageAttachments#isScreenshotAttachable.
15. Remove com.atlassian.jira.issue.managers.DefaultAttachmentManager#isScreenshotAppletEnabled if possible.
16. Remove com.atlassian.jira.issue.managers.DefaultAttachmentManager#isScreenshotAppletSupportedByOS if possible.
17. Make sure com.atlassian.jira.web.action.issue.ManageAttachments still works (lots was deleted).
18. Make sure JIRA.Dialogs#attachScreenshot() is unused.
    • ✔︎ not in jira
19. Find and kill a.issueaction-attach-screenshot.
    • ✔︎ actually keep it, it's used in issue-nav-components testdata, so i've renamed jira-html5-attach-images's issueaction-attach-image class to issueaction-attach-screenshot
20. Find and kill #attach-screenshot-window.
    • ✔︎ not in jira
    • ✔︎ not in jira-html5-attach-images
21. Remove attach screenshot analytics (key attach.screenshot.display, file includes/jira/issue/attachScreenshot.js). Update the event dictionary the note its removal.
    • ✔︎ not in jira
    • ✔︎ removed from analytics-whitelist
22. Remove any reference to jira.webresources:attach-screenshot-resources.
    • ✔︎ not in jira
    • ✔︎ not in jira-html5-attach-images
23. Ensure the new AT in jira-html5-attach-images actually runs.
    • ✔︎ it's not actually an AT, it's just a func test.
24. Setup CI plan to run func tests for jira-html5-attach-images
25. Ensure QUnit CI plan doesn't run the func tests for jira-html5-attach-images.
26. Ensure CI bundled tests include the jira-html5-attach-images func test.
27. Bump the JIRA dependency version in jira-html5-attach-images
28. Breaking API changes are reflected on Preparing for 7.0 docs.