Resolve "Cleanup validate_lfs_object_access feature flag"

What does this MR do and why?

This MR is to cleanup the validate_lfs_object_access feature flag, after the feature flag has been enabled by default for an appropriate amount of time in production. Related to: [Feature Flag] rollout of `validate_lfs_object_... (#547584 - closed)

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Related to #554670 (closed)