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
Ryan pointed out that it's safe to do this because we have the
G_DBUS_SEND_MESSAGE_FLAGS_PRESERVE_SERIAL flag and that it simplifies
how filter functions work.
Signed-off-by: David Zeuthen <davidz@redhat.com>