renderer: introduce destroy callback

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
diff --git a/src/compositor-headless.c b/src/compositor-headless.c
index d23ee0a..03bd0a4 100644
--- a/src/compositor-headless.c
+++ b/src/compositor-headless.c
@@ -141,7 +141,7 @@
 {
 	struct headless_compositor *c = (struct headless_compositor *) ec;
 
-	noop_renderer_destroy(ec);
+	ec->renderer->destroy(ec);
 
 	weston_seat_release(&c->fake_seat);
 	weston_compositor_shutdown(ec);