subcmds: delete redundant dest= settings

Add a test to enforce this too.

Change-Id: I80b5cf567aa33db9c24b53428c66d69f9c1d8d74
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/478481
Commit-Queue: Mike Frysinger <vapier@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Scott Lee <ddoman@google.com>

subcmds/selfupdate.py

@@ -54,7 +54,6 @@ need to be performed by an end-user.
         )
         g.add_option(
             "--repo-upgraded",
-            dest="repo_upgraded",
             action="store_true",
             help=optparse.SUPPRESS_HELP,
         )