Replace custom override schema with per-desktop override

GSettings now recognizes per-desktop overrides that can be used
to change schemas' default values for a particular desktop. This
is not entirely unlike our existing custom override mechanism in
mutter, except that it is not limited to keys in org.gnome.mutter,
and it doesn't require a separate schema - the latter means that
we (and gnome-teak-tool) no longer have to figure out the correct
schema for the current login session and just use the original one.

https://bugzilla.gnome.org/show_bug.cgi?id=786496

src/main.c

@@ -31,8 +31,6 @@ extern GType gnome_shell_plugin_get_type (void);
 #define SHELL_DBUS_SERVICE "org.gnome.Shell"
 #define MAGNIFIER_DBUS_SERVICE "org.gnome.Magnifier"
 
-#define OVERRIDES_SCHEMA "org.gnome.shell.overrides"
-
 #define WM_NAME "GNOME Shell"
 #define GNOME_WM_KEYBINDINGS "Mutter,GNOME Shell"
 
@@ -172,26 +170,6 @@ shell_dbus_init (gboolean replace)
   g_object_unref (session);
 }
 
-static void
-shell_prefs_init (void)
-{
-  ShellGlobal *global = shell_global_get ();
-  GSettings *settings = shell_global_get_overrides_settings (global);
-  GSettingsSchema *schema;
-  char **keys, **k;
-
-  if (!settings)
-    return;
-
-  g_object_get (G_OBJECT (settings), "settings-schema", &schema, NULL);
-
-  for (keys = k = g_settings_schema_list_keys (schema); *k; k++)
-    meta_prefs_override_preference_schema (*k, g_settings_schema_get_id (schema));
-
-  g_strfreev (keys);
-  g_settings_schema_unref (schema);
-}
-
 static void
 shell_introspection_init (void)
 {
@@ -509,8 +487,6 @@ main (int argc, char **argv)
 
   _shell_global_init ("session-mode", session_mode, NULL);
 
-  shell_prefs_init ();
-
   dump_gjs_stack_on_signal (SIGABRT);
   dump_gjs_stack_on_signal (SIGFPE);
   dump_gjs_stack_on_signal (SIGIOT);