Fixing lite build

Summary: Fixing lite build broke in unit test. `FilesPerLevel()` depends on `DB::GetProperty()`, which lite build doesn't support.

Test Plan: OPT=-DROCKSDB_LITE make check -j64

Reviewers: sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57651

db/db_iterator_test.cc

@@ -1557,7 +1557,9 @@ TEST_F(DBIteratorTest, ReadAhead) {
     Put(Key(i), value);
   }
   ASSERT_OK(Flush());
+#ifndef ROCKSDB_LITE
   ASSERT_EQ("1,1,1", FilesPerLevel());
+#endif  // !ROCKSDB_LITE
 
   env->random_read_bytes_counter_ = 0;
   options.statistics->setTickerCount(NO_FILE_OPENS, 0);