Merge branch 'delete-old-feature-flags-json_wrapper_legacy_mode' into 'master'

Delete the `json_wrapper_legacy_mode` feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/161727



Merged-by: Igor Drozdov <idrozdov@gitlab.com>
Approved-by: Igor Drozdov <idrozdov@gitlab.com>
Co-authored-by: Dylan Griffith <dyl.griffith@gmail.com>