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

gobject/gvalue.c

@@ -79,8 +79,6 @@
  *   GValue b = G_VALUE_INIT;
  *   const gchar *message;
  *
- *   g_type_init ();
- *
  *   /* The GValue starts empty */
  *   g_assert (!G_VALUE_HOLDS_STRING (&a));
  *