When there a large number of discussions on diffs, the instrumentation
has a significant impact on performance since it's often run in a tight
loop for line position calculation etc. We should disable this since
there are other ways to benchmark performance.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/52898
This commit fixes the following error in development:
ArgumentError: A copy of Gitlab::Metrics::Transaction has been
removed from the module tree but is still active!
