Remove merge_request_draft_filter feature flag
What does this MR do?
This feature flag was already enabled since 13.4 and can be removed now.
Does this MR meet the acceptance criteria?
Conformity
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I have included changelog trailers, or none are needed. (Does this MR need a changelog?) -
I have self-reviewed this MR per code review guidelines. -
I have followed the style guides.
Availability and Testing
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I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
Related to #298776 (closed)