Remove deployment feature flags

What does this MR do?

This removes the feature flags used for recording deployed merge requests and for displaying this data in the merge request widget. Both features are deemed stable now, so we no longer need these feature flags.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.