git: Don't use refs/tags/ on initial clone, part 3.

_verifyRefPresent was also broken for tag-based checkouts.  Since this
already uses determinePreferredCheckoutSource, which already used
refs/tags/ for tags, this code also doubled-up on tag names.

This whole code path would be a great candidate for that test suite
under t/ if I can ever get it polished up one day :(

To avoid commit spam, I've tested this on my own Qt module directories
by deleting them and forcing them to be checked-out with tags.

modules/ksb/Updater/Git.pm

@@ -73,9 +73,7 @@ sub _verifyRefPresent
 
     return 1 if pretending();
 
-    my $ref = (($commitType eq 'branch') ? 'refs/heads/'
-            : ($commitType eq 'tag')    ? 'refs/tags/'
-            : '') . $commitId;
+    my $ref = $commitId;
 
     my $hashref = run_forked("git ls-remote --exit-code $repo $ref",
         { timeout => 10, discard_output => 1, terminate_on_parent_sudden_death => 1});