repo: fix unused variable usage

The refactoring here left behind a variable reference that no
longer exists.  Clean it up.

Bug: https://crbug.com/gerrit/11144
Change-Id: Ifdb7918b37864c48f3deef27c8bae3f793275d35
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/236613
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Mike Frysinger <vapier@google.com>