Merge branch 'acook/code_generation_anthropic_enabled_default' into 'master'

Remove code_generation_anthropic feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/139456



Merged-by: Jan Provaznik <jprovaznik@gitlab.com>
Approved-by: Jan Provaznik <jprovaznik@gitlab.com>
Reviewed-by: Jan Provaznik <jprovaznik@gitlab.com>
Co-authored-by: Allen Cook <acook@gitlab.com>