Jira Installer - content is duplicated on Upgrade Checklist step

Issue Summary

In the recent version we have introduced a new bug in Jira installer. On the step "Upgrade Checklist" content is duplicated and can confuse the user. More seasoned administrators might remember that the checklist needs to be confirmed before proceeding, but it might confuse new users. This bug is more inpactuful on Windows installation because of the UI.

This is reproducible on the Data Center: Yes

Steps to Reproduce

1. Set up Jira Software DC on Windows, for example, version 9.4.x.
2. Upgrade to Jira Software 9.15 using the installer method.
3. Opt-in to upgrade the existing installation and point to the installation directory.
4. On the step "Upgrade Checklist," user is unable to click the "Upgrade" button and proceed with the upgrade because checkbox "I've completed all these steps!" is not checked. This checkbox is not visible on the screen.

Expected Results

• The "Upgrade Checklist" page content is not duplicated.
• "I've completed all these steps!" checkbox is visible to the user.

Actual Results

• Windows - The "I've completed all these steps!" checkbox is visible on the screen and there is no vertical scroll. More seasoned administrators might remember that there should be checkbox input, but the user would be blocked from proceeding with the installer wizard.
  
• Linux - The "Upgrade Checklist" content is printed twice on the terminal and the last prompt is "Have you completed all these steps?". Users can proceed with the upgrade by confirming.
  

Workaround

Windows:

• The user must manually drag the bounds of the installer window vertically to see and check the  "I've completed all these steps!" checkbox. This is not immediately obvious because there is no vertical scroll control.
  
• Once the checkbox is checked, user can finally click on the button and proceed with the upgrade.

Linux

• Simply ignore duplicated content and confirm the upgrade by answering "Yes".

Thank you
Kind Regards