Pass --help to the most nested subcommand

'ostree admin <x> --help' and 'ostree admin instutil <x> --help' should
give help on the deepest subcommand, not on 'ostree admin'.

https://bugzilla.gnome.org/show_bug.cgi?id=737194

src/ostree/ot-admin-builtin-instutil.c

@@ -117,7 +117,7 @@ ot_admin_builtin_instutil (int argc, char **argv, OstreeSysroot *sysroot, GCance
 
   argc = out;
 
-  if (subcommand_name == NULL || want_help)
+  if (subcommand_name == NULL)
     {
       subcommand = admin_instutil_subcommands;
       g_print ("usage: ostree admin instutil COMMAND [options]\n");

src/ostree/ot-builtin-admin.c

@@ -145,7 +145,7 @@ ostree_builtin_admin (int argc, char **argv, OstreeRepo *repo, GCancellable *can
 
   argc = out;
 
-  if (subcommand_name == NULL || want_help)
+  if (subcommand_name == NULL)
     {
       subcommand = admin_subcommands;
       g_print ("usage: ostree admin --sysroot=PATH COMMAND [options]\n");