gitlab-ce: Remove 'deltas only' from Gitlab::Git::DiffCollection

~Conversation #222 (closed)

• provide an alternative and update all call sites in gitlab-ce https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11201
• wait for new method to be merge into gitlab-ee master
• update call sites in gitlab-ee https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1854
• remove 'deltas only' code from DiffCollection https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11285