Fix flaky DBTest2.RateLimitedCompactionReads (#9185)

Summary:
DBTest2.RateLimitedCompactionReads sometime shows following failure:

  what():  db/db_test2.cc:3976: Failure
Expected equality of these values:
  i + 1
    Which is: 4
  NumTableFilesAtLevel(0)
    Which is: 0

The assertion itself doesn't appear to be correct. Fix it.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9185

Test Plan: Removing an assertion shouldn't break anything.

Reviewed By: ajkr

Differential Revision: D32549530

fbshipit-source-id: 9993372d8af89161f903337a13f3e316e690a6b8

db/db_test2.cc

@@ -3973,7 +3973,9 @@ TEST_F(DBTest2, RateLimitedCompactionReads) {
         ASSERT_OK(Put(Key(j), DummyString(kBytesPerKey)));
       }
       ASSERT_OK(dbfull()->TEST_WaitForFlushMemTable());
-      ASSERT_EQ(i + 1, NumTableFilesAtLevel(0));
+      if (i + 1 < kNumL0Files) {
+        ASSERT_EQ(i + 1, NumTableFilesAtLevel(0));
+      }
     }
     ASSERT_OK(dbfull()->TEST_WaitForCompact());
     ASSERT_EQ(0, NumTableFilesAtLevel(0));