[Feature flag cleanup] Block merging if there are failed status checks
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## Summary
This issue is to cleanup the `only_allow_merge_if_all_status_checks_passed` feature flag, after the feature flag has been enabled by default for an appropriate amount of time in production.
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## Owners
- Team: ~"group::compliance"
- Most appropriate slack channel to reach out to: `#g_manage_compliance`
- Best individual to reach out to: `@dftian`
- PM: `@stkerr`
## Stakeholders
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- The Support Team
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## Expectations
### What might happen if this goes wrong?
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### Cleaning up the feature flag
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- [x] Create a merge request to remove `only_allow_merge_if_all_status_checks_passed` feature flag. Ask for review and merge it.
- [x] Remove all references to the feature flag from the codebase.
- [x] Remove the YAML definitions for the feature from the repository.
- [x] Create [a changelog entry](https://docs.gitlab.com/ee/development/feature_flags/#changelog).
- [x] Ensure that the cleanup MR has been deployed to both production and canary.
If the merge request was deployed before [the code cutoff](https://about.gitlab.com/handbook/engineering/releases/#self-managed-releases-1),
the feature can be officially announced in a release blog post.
- [x] `/chatops run auto_deploy status 00693c880db0c069124029f6b075ac2bc5611b1e`
- [x] Close [the feature issue](ISSUE LINK) to indicate the feature will be released in the current milestone.
- [x] If not already done, clean up the feature flag from all environments by running these chatops command in `#production` channel:
- [x] `/chatops run feature delete only_allow_merge_if_all_status_checks_passed --dev`
- [x] `/chatops run feature delete only_allow_merge_if_all_status_checks_passed --staging`
- [x] `/chatops run feature delete only_allow_merge_if_all_status_checks_passed`
- [x] Close this rollout issue.
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