Cleanup api_caching_releases feature flag [RUN ALL RSPEC] [RUN AS-IF-FOSS]

NOTE: This is an urgent MR in the context.

What does this MR do?

We've confirmed that the feature is deemed stable, therefore removing the feature flag.

Close #257852 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

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

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