Release Environment - Drop feature flag release_environment

In #19580 (closed) via gitlab-org/release-tools!2876 (merged), we automated the release environment creation. During the process, we added a new feature flag release_environment to be able to disable the new change quickly when something goes wrong.

After running the feature for some time, once we have the confidence that it is working well, we should drop the feature flag.

Exit Criteria

• Drop FF release_environment from the codebase gitlab-org/release-tools!4161 (merged)
• Drop the feature flag com ops