libweston: don't clean up surface role

Surface roles are permanent, so it should not be cleaned up.

Fixes: #409
weston: ../libweston/compositor.c:4094: weston_surface_set_role: Assertion `role_name' failed.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>

libweston/touch-calibration.c

@@ -360,8 +360,6 @@ destroy_touch_calibrator(struct wl_resource *resource)
 
 	if (calibrator->surface) {
 		unmap_calibrator(calibrator);
-		weston_surface_set_role(calibrator->surface, NULL,
-					calibrator->surface->resource, 0);
 		wl_list_remove(&calibrator->surface_destroy_listener.link);
 		wl_list_remove(&calibrator->surface_commit_listener.link);
 	}