Remove incorrect assertion and supporting code

Children can exist when destroying a container, such as when destroying
the last output. Sway is not terminating in that case.

include/sway/server.h

@@ -47,8 +47,6 @@ struct sway_server {
 
 	bool debug_txn_timings;
 
-	bool terminating;
-
 	struct sway_transaction *head_transaction; // singly linked list
 
 	// When a view is being destroyed and is waiting for a transaction to

sway/main.c

@@ -34,7 +34,6 @@ struct sway_server server;
 void sway_terminate(int exit_code) {
 	terminate_request = true;
 	exit_value = exit_code;
-	server.terminating = true;
 	wl_display_terminate(server.wl_display);
 }
 

sway/tree/container.c

@@ -319,15 +319,6 @@ struct sway_container *container_destroy_noreaping(struct sway_container *con) {
 		}
 	}
 
-	// At this point the container being destroyed shouldn't have any children
-	// unless sway is terminating.
-	if (!server.terminating) {
-		if (!sway_assert(!con->children || con->children->length == 0,
-					"Didn't expect to see children here")) {
-			return NULL;
-		}
-	}
-
 	con->destroying = true;
 	list_add(server.destroying_containers, con);