docs: remove feature flag references for hooks
This change is a quick update of the docs to remove condition language required when the feature flags were around to migrate from Ruby to Go.
The 17.0 major release is coming on May 16, 2024! This version brings many exciting improvements to GitLab, but also removes some deprecated features. We are introducing three breaking change windows during which we expect breaking changes to be deployed to GitLab.com. You can read more about it on our blogpost. The second breaking change window begins 2024-04-29 09:00 UTC and ends 2024-05-01 22:00 UTC.
This change is a quick update of the docs to remove condition language required when the feature flags were around to migrate from Ruby to Go.