fix: slight optimization for dtor mvcc

Author: yuujin-Q

txn/mvcc_storage.cc

@@ -15,7 +15,11 @@ void MVCCStorage::InitStorage() {
 MVCCStorage::~MVCCStorage() {
   for (unordered_map<Key, deque<Version*>*>::iterator it = mvcc_data_.begin();
        it != mvcc_data_.end(); ++it) {
-    delete it->second;          
+    auto version_list = it->second;
+    for (auto version : *version_list) {
+      delete version;
+    }
+    delete version_list;          
   }
 
   mvcc_data_.clear();

txn/txn_processor_test.cc

@@ -92,6 +92,10 @@ void Benchmark(const vector<LoadGen *> &lg)
        mode <= MVCC;
        mode = static_cast<CCMode>(mode + 1))
   {
+    // FILTER modes for testing
+    // if (mode != SERIAL && mode != MVCC) {
+    //   continue;
+    // }
         // Print out mode name.
     cout << ModeToString(mode) << flush;