swh.lister.gitlab: Remove TODO about the 403 response code

Multiple issues wish for the api to converge on 429 but nothing is
clear nor documented yet:
- https://gitlab.com/gitlab-com/infrastructure/issues/348
- https://gitlab.com/gitlab-org/gitlab-ce/issues/41309
- https://gitlab.com/gitlab-org/gitlab-ce/issues/46522

The only response code mentioned in the documentation is
403 (https://docs.gitlab.com/ee/api/README.html#status-codes).

swh/lister/gitlab/lister.py

@@ -91,8 +91,6 @@ class GitLabLister(SWHPagingHttpLister):
 
         """
         reqs_remaining = int(response.headers['RateLimit-Remaining'])
-        # TODO: need to dig further about the actual returned code
-        # (not seen yet in documentation)
         if response.status_code == 403 and reqs_remaining == 0:
             reset_at = int(response.headers['RateLimit-Reset'])
             delay = min(reset_at - time.time(), 3600)