This commit makes it possible for
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14420 to handle
multiple SAML providers.

Updated users API documentation
Moved API level changes to the service level

These can just be `delete` calls, with the caveat that it only takes one
argument.

This can be done trough the API for the current user, or on the
profile page.

Partially addresses #47424.

Closes #37073