Revert "Synchronize the default branch when updating a remote mirror"

Merged Bob Van Landuyt requested to merge bvl-fix-11-3-default-branch-reset into 11-3-stable-ee-patch-6

What does this MR do?

This makes sure the default branch is not being reset when repository mirroring is enabled

What are the relevant issue numbers?

Closes: https://gitlab.com/gitlab-org/gitlab-ee/issues/8003

Does this MR meet the acceptance criteria?

Edited by Bob Van Landuyt