Delete the usage_data_api feature flag

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143973



Merged-by: Hordur Freyr Yngvason <hfyngvason@gitlab.com>
Approved-by: Gavin Hinfey <ghinfey@gitlab.com>
Approved-by: Sebastian Rehm <srehm@gitlab.com>
Approved-by: Hordur Freyr Yngvason <hfyngvason@gitlab.com>
Co-authored-by: Rémy Coutable <remy@rymai.me>