main: Move NO_AT_BRIDGE hack to mutter

There is no guarantee that it'll have effect, since the time anything
that'll look at that environment variable is not known by gnome-shell.
Let mutter carry this burden instead.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1710>

src/main.c

@@ -465,10 +465,7 @@ main (int argc, char **argv)
   meta_set_wm_name (WM_NAME);
   meta_set_gnome_wm_keybindings (GNOME_WM_KEYBINDINGS);
 
-  /* Prevent meta_init() from causing gtk to load the atk-bridge*/
-  g_setenv ("NO_AT_BRIDGE", "1", TRUE);
   meta_init ();
-  g_unsetenv ("NO_AT_BRIDGE");
 
   /* FIXME: Add gjs API to set this stuff and don't depend on the
    * environment.  These propagate to child processes.