Fix RocksDB Lite build (facebook#4675)

Summary:
Our internal CI test caught RocksDB Lite build failures. The failures are due to a new test introduced in facebook#4665 using `SSTFileWriter` and `IngestExternalFile`, but these is not exposed under lite mode. Fixed by #ifdef'ing out the test.

```
db/db_test2.cc: In member function ‘virtual void rocksdb::DBTest2_TestCompactFiles_Test::TestBody()’:
db/db_test2.cc:2907:3: error: ‘SstFileWriter’ is not a member of ‘rocksdb’
   rocksdb::SstFileWriter sst_file_writer{rocksdb::EnvOptions(), options};
   ^
In file included from ./util/testharness.h:15:0,
                 from ./table/mock_table.h:23,
                 from ./db/db_test_util.h:44,
                 from db/db_test2.cc:13:
db/db_test2.cc:2912:13: error: ‘sst_file_writer’ was not declared in this scope
   ASSERT_OK(sst_file_writer.Open(external_file1));
```
Pull Request resolved: facebook#4675

Differential Revision: D13035984

Pulled By: sagar0

fbshipit-source-id: c1ceac550dfac1a85eeea436693dc7dd467519a6

db/db_test2.cc

@@ -2888,6 +2888,7 @@ TEST_F(DBTest2, TestGetColumnFamilyHandleUnlocked) {
   rocksdb::SyncPoint::GetInstance()->ClearAllCallBacks();
 }
 
+#ifndef ROCKSDB_LITE
 TEST_F(DBTest2, TestCompactFiles) {
   // Setup sync point dependency to reproduce the race condition of
   // DBImpl::GetColumnFamilyHandleUnlocked
@@ -2946,6 +2947,7 @@ TEST_F(DBTest2, TestCompactFiles) {
   rocksdb::SyncPoint::GetInstance()->DisableProcessing();
   rocksdb::SyncPoint::GetInstance()->ClearAllCallBacks();
 }
+#endif  // ROCKSDB_LITE
 
 }  // namespace rocksdb