Fix an ASAN error in transaction_test.cc

Summary:
One test in transaction_test.cc forgets to call SyncPoint::DisableProcessing().
As a result, a program might to access the SyncPoint singleton after it
already goes out of scope.

This patch fix this error by calling SyncPoint::DisableProcessing().

Test Plan: transaction_test

Reviewers: sdong, IslamAbdelRahman, kradhakrishnan, anthony

Reviewed By: anthony

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D54033

utilities/transactions/transaction_test.cc

@@ -2876,6 +2876,7 @@ TEST_F(TransactionTest, ExpiredTransactionDataRace1) {
   ASSERT_EQ("1", value);
 
   delete txn1;
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
 }
 
 }  // namespace rocksdb