Fix TransactionTest::SeqAdvanceTest ASAN failure

Summary:
The test didn't delete txn before creating a new one.
Closes https://github.com/facebook/rocksdb/pull/2913

Differential Revision: D5880236

Pulled By: yiwu-arbug

fbshipit-source-id: 7a4fcaada3d86332292754502cd8f4341143bf4f

utilities/transactions/transaction_test.cc

@@ -4703,6 +4703,7 @@ TEST_P(TransactionTest, SeqAdvanceTest) {
   ASSERT_OK(s);
   seq = db_impl->GetLatestSequenceNumber();
   ASSERT_EQ(exp_seq, seq);
+  delete txn;
 
   // Commit without prepare. It shoudl write to DB without a commit marker.
   txn = db->BeginTransaction(write_options, txn_options);