Revert 'Restrict access to branch release-R121 to LTS Refresher group.'

This reverts commit b268ef01285f8dcb8092e7e16a3b8aabe685e7b9.

Reason for revert: Finished LTS refresh.

Change-Id: I9f7b6fe6ea6cd2a083dbcff64a987eea62fee44c
Reviewed-on: https://cos-review.googlesource.com/c/All-Projects/+/151324
Reviewed-by: Kevin Berry <kpberry@google.com>
Tested-by: Miri Amarilio <mirilio@google.com>