Remove matrix_docker_network references from remove-all script

roles/custom/matrix-base/templates/bin/remove-all.j2

@@ -26,9 +26,6 @@ else
 	echo "Remove unused Docker images and resources"
 	docker system prune -af
 
-	echo "Remove Docker matrix network (should be gone already, but ..)"
-	docker network rm {{ matrix_docker_network }}
-
 	echo "This playbook creates a lot of matrix-* networks. Consider removing them manually ('docker network ls', followed by 'docker network rm NETWORK_NAME')"
 
 	echo "Remove {{ matrix_base_data_path }} directory"