fix(plasmusic-toolbar): remove unused preferredPlayerIdentity config …

…to prevent error (#405)

Removed `preferredPlayerIdentity` assignment from `plasmusic-toolbar` module to fix DBus error caused by an incomplete config parameter.
The error occurred during the application of desktop scripts, generating an invalid config line in `preferredPlayerIdentity`.

modules/widgets/plasmusic-toolbar.nix

@@ -265,7 +265,6 @@ in
           else if source == "auto" then
             {
               choosePlayerAutomatically = true;
-              preferredPlayerIdentity = null;
             }
           else
             {