There is no way in git to efficiently tell if a commit has been
reverted. Instead, GitLab creates system notes when we perform this
action in the web UI. These are introspected to answer the question;
doing so requires us to extract commit references from those notes.

With this change, we stop extracting commit references from the message
of the commit that is under question. This is user-controlled content
and we can't control the number of references in it. Further, since the
revert happens *after* that commit message is written, there is no way
for it to contain references to a reverting commit.