Revert PR 10777 "Fix FIFO causing overlapping seqnos in L0 files due to overla…"

[hx235]

Context/Summary:

This reverts commit fc74abb and related HISTORY record.

The issue with PR 10777 or general approach using earliest_mem_seqno like #5958 (comment) is that the earliest seqno of memtable of each CF will always start with 0 upon Recover(). It is only updated to the correct value when there is unflushed data from previous db session or a new memtable is created. If neither of these happen, it will lead to false positive overlapping seqno and PR 10777 will throw something like https://github.com/facebook/rocksdb/blob/main/db/compaction/compaction_picker.cc#L1002-L1004. See Test for a repro.

A quick fix like 3e583a8 might work. However this solution needs more testing.

Luckily a more elegant and complete solution #10922 to the overlapping seqno problem these PRs aim to solve does not have above problem. It is already being pursued and in the process of review. So we can just revert this PR 10777 and focus on getting PR 10922 to land.

Test:

• Repro

TEST_F(DBCompactionTest, Repro) {
  Options options = CurrentOptions();
  options.force_consistency_checks = true;
  options.compression = kNoCompression;
  options.compaction_style = CompactionStyle::kCompactionStyleLevel;
  options.disable_auto_compactions = true;

  DestroyAndReopen(options);
  ASSERT_OK(Put("key1", "v"));
  ASSERT_OK(Put("key2", "v"));
  ASSERT_OK(Flush());
  ASSERT_EQ(1, NumTableFilesAtLevel(0));

  ASSERT_OK(Put("key3", "v"));
  ASSERT_OK(Put("key4", "v"));
  ASSERT_OK(Flush());
  ASSERT_EQ(2, NumTableFilesAtLevel(0));

  Reopen(options);

  ColumnFamilyMetaData cf_meta_data;
  db_->GetColumnFamilyMetaData(&cf_meta_data);
  assert(cf_meta_data.levels[0].files.size() == 2);
  std::vector<std::string> input_files;
  for (const auto& file : cf_meta_data.levels[0].files) {
    input_files.push_back(file.name);
  }
  // Just a normal CompactFiles() which should pass but now fail due to false positive caught by #PR 10777
  Status s = db_->CompactFiles(CompactionOptions(), input_files, 0);
  EXPECT_TRUE(s.IsAborted());
  EXPECT_TRUE(s.ToString().find(
                  "has overlapping seqnos with earliest memtable seqnos") !=
              std::string::npos);
}

• make check

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