Fix double frees in Wayland 1.2

Remove double frees in destroy_func generated by qwaylandscanner. The
wl_resource struct is already freed by wl_resource_destroy() in
wayland-server in Wayland 1.2.

Change-Id: Ibd42e42a23238ba9c665a7c918f9b547968f7146
Reviewed-by: Andy Nichols <andy.nichols@digia.com>