Drop GFM support in Issue/MergeRequest in Milestone
Drop GFM support in Issue/MergeRequest in Milestone page to speed up page rendering.
Milestone page with many issues and/or merge requests (typically 30-100) is extremely slow (meta: #33885 (moved)) due to GFM support of their title there. Even on Issues and Merge Requests page, the title of each issue/merge request does not have GFM support, so we should drop GFM support on Milestone page both for the consistency and performance.
Links / references
Meta: #33885 (moved)