Remove deprecated g_thread_init usage

From the docs:
  `g_thread_init` has been deprecated since version 2.32 and should not
  be used in newly-written code. This function is not longer necessary.
  The GLib threading system is automatically initialized at the start of
  your program.

luakit.c

@@ -170,8 +170,6 @@ main(gint argc, gchar *argv[]) {
     }
 
     gtk_init(&argc, &argv);
-    if (!g_thread_supported())
-        g_thread_init(NULL);
 
     init_directories();
     init_lua(uris);