fix(codes/cpp): Memory leak fix: the space was not freed when pop removed the element. (#423)

codes/cpp/chapter_stack_and_queue/linkedlist_deque.cpp

@@ -92,6 +92,7 @@ public:
             if (fNext != nullptr) {
                 fNext->prev = nullptr;
                 front->next = nullptr;
+                delete front;
             }
             front = fNext;   // 更新头结点
         // 队尾出队操作
@@ -102,6 +103,7 @@ public:
             if (rPrev != nullptr) {
                 rPrev->next = nullptr;
                 rear->prev = nullptr;
+                delete rear;
             }
             rear = rPrev;    // 更新尾结点
         }