jalv-qt: move override out of top-level to reduce thunks (#431187)

pkgs/by-name/ja/jalv-qt/package.nix

···
+{
+  jalv,
+}:
+
+jalv.override {
+  useQt = true;
+}

pkgs/top-level/all-packages.nix

···
   jackmix = libsForQt5.callPackage ../applications/audio/jackmix { };
   jackmix_jack1 = jackmix.override { jack = jack1; };
 
-  jalv-qt = jalv.override { useQt = true; };
-
   js8call = qt5.callPackage ../applications/radio/js8call { };
 
   jwm = callPackage ../applications/window-managers/jwm { };