Remove undefined method for default module handling.

This was changed some time ago to pull from kdesrc-buildrc-sample if no
other config was defined, which ended up removing the method being
called here. But I didn't remove all usages of that method, which was
caught by a user yesterday.

kdesrc-build

@@ -7314,7 +7314,7 @@ sub read_options
     # If the user doesn't ask to build any modules, build a default set.
     # The good question is what exactly should be built, but oh well.
     if ($using_default) {
-        $ctx->setup_default_modules();
+        warning (" b[y[*] There do not seem to be any modules to build in your configuration.");
         return ();
     }