compositor: Remove notion of primary renderer

Uploading textures are done by what outputs intersect the surface,
not an arbitrary renderer. If no outputs intersect the surface, the
source buffer is locked for longer until the surface is shown, at which
point a renderer will be uploaded the buffer.

examples/scene-graph.c

@@ -166,8 +166,7 @@ int main(int argc, char *argv[]) {
 	server.allocator = wlr_allocator_autocreate(server.backend,
 		server.renderer);
 
-	struct wlr_compositor *compositor =
-		wlr_compositor_create(server.display, server.renderer);
+	struct wlr_compositor *compositor = wlr_compositor_create(server.display);
 
 	wlr_xdg_shell_create(server.display, 2);