Merge branch 'fix/issue-39679-remove-completed-feature-flags' into 'main'

Remove completed-rollout feature flags (FF_USE_NEW_BASH_EVAL_STRATEGY, FF_SKIP_NOOP_BUILD_STAGES, FF_SET_PERMISSIONS_BEFORE_CLEANUP)

Closes #39679

See merge request https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/7144

Merged-by: Adebayo Adesanya <aadesanya@gitlab.com>
Approved-by: Vishal Tak <vtak@gitlab.com>
Approved-by: Roshni Sarangadharan <rsarangadharan@gitlab.com>
Co-authored-by: Duo Developer <service_account_group_9970_1976e9ecde3c53c783b64edb9ae993eb@noreply.gitlab.com>