Remove auto_close_issues_stop_using_commit_author FF

Mario Celirequested to merge
545166-remove-feature-flag into master

What does this MR do and why?

Now pushing directly to a repository's default branch will use the pushing user to perform actions like automatically closing issues. This MR simply removes the feature flag that has been enabled globally in production since #557942 (comment 2668042316)

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Related to #545166 (closed)

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