gtk: rely on default marshallers

Similar to previous removals of g_cclosure_marshal_VOID__VOID we can remove
other marshallers for which are a simple G_TYPE_NONE with single parameter.
In those cases, GLib will setup both a c_marshaller and va_marshaller for
us. Before this commit, we would not get a va_marshaller because the
c_marshaller is set.

Related to GNOME/Initiatives#10

gdk/gdkdevice.c

@@ -367,7 +367,7 @@ gdk_device_class_init (GdkDeviceClass *klass)
                   G_TYPE_FROM_CLASS (object_class),
                   G_SIGNAL_RUN_LAST,
                   0, NULL, NULL,
-                  g_cclosure_marshal_VOID__OBJECT,
+                  NULL,
                   G_TYPE_NONE, 1, GDK_TYPE_DEVICE_TOOL);
 }