bitbake: bin/git-make-shallow: Fix syntax to work with older git versions

The transaction model was only introduced in git 2.27 whereas Ubuntu focal
(20.04) has 2.25. This causes failures. We don't need the transations here
so simply drop the commit piece, fixing on older git versions.

Credit to Nick Owens <nick.owens@eero.com> for working out how to fix it.

(Bitbake rev: 0723ec9d4cd7c9b2d46904c3a038be123feea374)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/git-make-shallow

@@ -116,7 +116,7 @@ def filter_refs(refs):
     to_remove = set(all_refs) - set(refs)
     if to_remove:
         check_output(git_cmd + ['update-ref', '--no-deref', '--stdin', '-z'],
-                     input=''.join('delete ' + l + '\0\0' for l in to_remove) + 'commit\0')
+                     input=''.join('delete ' + l + '\0\0' for l in to_remove))
 
 
 def follow_history_intersections(revisions, refs):