communication: remove memory leak

prog/communication.py

@@ -117,6 +117,7 @@ class Client():
             id = head["id"]
             assert id in self.waiting_questions
             q = self.waiting_questions[id]
+            del self.waiting_questions[id]
             q.future.set_result((head, data_raw))
 
     async def question(self, head, data):