Bug: Allow MR comment thread to be deleted when there is single commit reference

Steps to reproduce

1. Open any MR threads
2. Make some code changes which should generate commit reference to that thread
3. Login as Admin/Maintainer access account to same repository and go to that MR thread
4. Delete all the thread comments

Current behavior:

• Thread is still showing up as open and it has only the commit reference and there is no way to delete that.

Expected behavior:

• It should be allowed for Maintainer or Admin access accounts to delete such thread as well

Reference:

• There are not three dots option to delete