I'm not clear - is there some way to remove "Rank (Obsolete)" at this point, and is it safe?

Version 7.1.4 and the field is still there.

Atlassian should automatically remove deprecated fields.

Atlassian, I'm really puzzled by this issue: Is it Atlassian's intention that JIRA users see this useless field forever? Why doesn't the upgrade just delete it?

Why hasn't this field been automatically removed from Cloud instances???

I had this issue recently and couldn't find the comments on the linked page. If you do have ScriptRunner installed, the script, that you can run from script console, is:

import com.atlassian.jira.bc.JiraServiceContextImpl
import com.atlassian.jira.bc.customfield.CustomFieldService
import com.atlassian.jira.component.ComponentAccessor

def customFieldManager = ComponentAccessor.customFieldManager
def customFieldService = ComponentAccessor.getComponent(CustomFieldService)

def currentUser = ComponentAccessor.getJiraAuthenticationContext().user
def serviceContext = new JiraServiceContextImpl(currentUser)

customFieldManager.getCustomFieldObjectsByName("Rank").findAll {
    it.customFieldType.descriptor.moduleClass.name == "com.atlassian.greenhopper.customfield.rank.RankCFType"
}.each { cf ->
    customFieldService.validateDelete(serviceContext, cf.idAsLong)

    def errors = serviceContext.errorCollection
    if (errors.hasAnyErrors()) {
        log.warn ("Can't delete field: ${cf.id}")
    }
    else {
        customFieldManager.removeCustomField(cf)
    }
}

You can find a KB entry at https://confluence.atlassian.com/display/AGILEKB/How+to+unlock+a+Locked+field but it required database modifications (not easily possible in a seciruty concerned company where JIRA admins are not the same as DB admins).
In the comments, there are solutions using a script runner, but this requires the additional plug-in to be installed.
I would prefer if the update would complete the job and unlock the fields, so a workaround is not necessary.

I agree with Hans – I don't mind deleting the field by hand, but it is locked and I can't puzzle out a way to unlock it.

This is less a task than a Bug, regarding that the upgrade documentation is inconsistent with the tool behavior (the user is not able to follow the "delete" instructions because the field is locked).

Actually, it is OK to let the user remove the field from the administration front-end and not auto-remove the field in the upgrade process.

But the user cannot delete the field because it is still locked.

So what is required instead, is that the upgrade removes the "locked" (managed) state of the obsoleted field, so the user has the possibility to delete the field if he wants from the administration frontend. Assuming the upgrade removed the "locked" (managed) state, the upgrade documentation will become correct again.

Thanks.