Fix c_test ASAN failure

Summary:
Fix c_test missing deletion of write batch pointer.
Closes https://github.com/facebook/rocksdb/pull/2725

Differential Revision: D5613866

Pulled By: yiwu-arbug

fbshipit-source-id: bf3f59a6812178577c9c25bae558ef36414a1f51

db/c_test.c

@@ -1387,6 +1387,7 @@ int main(int argc, char** argv) {
     rocksdb_writebatch_put(wb, "box", 3, "c", 1);
     rocksdb_writebatch_delete(wb, "bar", 3);
     rocksdb_transactiondb_write(txn_db, woptions, wb, &err);
+    rocksdb_writebatch_destroy(wb);
     CheckTxnDBGet(txn_db, roptions, "box", "c");
     CheckNoError(err);