Rename `Gitlab::Git::EncodingHelper` to `Gitlab::EncodingHelper`
Since in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11770 it is used outside the context of git.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Since in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11770 it is used outside the context of git.