Remove g_type_init() calls

Very many testcases, some GLib tools (resource compiler, etc) and
GApplication were calling g_type_init().

Remove those uses, as they are no longer required.

https://bugzilla.gnome.org/show_bug.cgi?id=686161

gio/tests/gdbus-connection-flush-helper.c

@@ -30,8 +30,6 @@ main (int   argc,
   GError *error;
   gboolean ret;
 
-  g_type_init ();
-
   error = NULL;
   c = g_bus_get_sync (G_BUS_TYPE_SESSION,
                       NULL, /* GCancellable* */