Signed-off-by: Rémy Coutable <remy@rymai.me>

Since the frontend for this feature isn't ready, better to hide the
confusing field behind a feature flag.

The status is shown for
- The author of a commit when viewing a commit
- Notes on a commit (regular/diff)
- The user that triggered a pipeline when viewing a pipeline
- The author of a merge request when viewing a merge request
- The author of notes on a merge request (regular/diff)
- The author of an issue when viewing an issue
- The author of notes on an issue
- The author of a snippet when viewing a snippet
- The author of notes on a snippet
- A user's profile page
- The list of members of a group/user

This reverts merge request !20679

Backports relevant changes made in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5163 to CE

We also try to unify the way we setup OmniAuth, and how we check
if it's enabled or not.

This method is unneeded given its been pushed to Gitaly, through
https://gitlab.com/gitlab-org/gitaly/merge_requests/780

Closes https://gitlab.com/gitlab-org/gitaly/issues/1235

This reverts commit 4d9a3f42, reversing
changes made to ecf9c145.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This allows us to check specific abilities in views, while still
enabling/disabling them at once.