The code can be always rolled back to empty, no need to save the old …

…code.

Because it's not allowed to overwrite code now.

libethereum/State.cpp

@@ -583,7 +583,7 @@ void State::rollback(size_t _savepoint)
             m_cache.erase(change.address);
             break;
         case Change::Code:
-            account.setCode(std::move(change.oldCode));
+            account.setCode(/*std::move(change.oldCode)*/bytes{});
             break;
         case Change::Touch:
             account.untouch();