Cut over coalesce ops (#4910)

Summary:
Pull Request resolved: #4910

X-link: facebookresearch/FBGEMM#1935

Cut over from fbgemm -> mslk for coalesce. Coalesce is only used in fbcode (not in xlformers), so the fbgemm code could be deleted right away.

Reviewed By: q10

Differential Revision: D82983166

fbshipit-source-id: 8584b17306fd73f87449f822c56378896033c04a

Author: cthi