Remove deploy trigger from omnibus-gitlab

After #717 (closed) is ready, we can remove the deploy trigger from omnibus-gitlab.

Consider doing this is a iterative fashion.

1. Disable it - don't remove the code => Set the AUTO_DEPLOY_OMNIBUS_TRIGGERS_DEPLOYER variable to false in https://dev.gitlab.org/gitlab/omnibus-gitlab/-/settings/ci_cd (see gitlab-org/omnibus-gitlab!4970 (merged) and gitlab-org/omnibus-gitlab!5001 (merged))
2. Enable release-tools tagging with omnibus_triggers_deployer feature flag
3. Enable/Test to validate release-tools is able to trigger as expected
4. Remove the unused code in omnibus
5. Remove the feature flag code in release-tools
6. remove AUTO_DEPLOY_OMNIBUS_TRIGGERS_DEPLOYER variable from omnibus dev
7. remove the omnibus_triggers_deployer feature flag from release-tools ops