Free non-legacy resources inside wl_resource_destroy

This commit makes wl_resource_destroy automatically free all non-legacy
resource structures.  Since wl_resource is now an opaque structure it
doesn't make sense for the clients to be freeing it.  This checks to make
sure that it was added through wl_client_add_object or wl_client_new_object
and not wl_client_add_resource before it frees it.  This way if it is a
legacy resources embedded in a structure somewhere we don't have an invalid
free.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>