gnome.mutter: remove unneeded dependencies

json-glib was removed in https://gitlab.gnome.org/GNOME/mutter/-/commit/03235773be11073efba0a98cffca635f8b6678a6
(part of bump in fde899eefd).

libcap-ng is not used at all. It was added in 9742df1595
required by an older version of the patch from https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/460
which was dropped in 8c5884ef4e.

Also update comment since mutter-clutter no longer depends on graphene, -cogl and -mtk libraries do.

pkgs/desktops/gnome/core/mutter/default.nix

@@ -10,7 +10,6 @@
 , colord
 , lcms2
 , pango
-, json-glib
 , libstartup_notification
 , libcanberra
 , ninja
@@ -59,7 +58,6 @@
 , sysprof
 , libsysprof-capture
 , desktop-file-utils
-, libcap_ng
 , egl-wayland
 , graphene
 , wayland
@@ -91,9 +89,7 @@ stdenv.mkDerivation (finalAttrs: {
   ];
 
   propagatedBuildInputs = [
-    # required for pkg-config to detect mutter-clutter
-    json-glib
-    libcap_ng
+    # required for pkg-config to detect mutter-mtk
     graphene
   ];