Delete unnecessary error logs with `TiDBEnableDistributeReorg`

[zimulala]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

tidb>  create table t(a int, b int);
tidb> set @@global.tidb_ddl_distribute_reorg = 'on';
tidb> alter table t add index idx(a);

2. What did you expect to see? (Required)

[2023/02/06 11:28:56.958 +00:00] [Info] [dist_backfilling.go:260] ["no backfill job, handle backfill task finished"]

3. What did you see instead (Required)

[2023/02/06 11:28:55.172 +00:00] [Error] [spmcpool.go:293] ["producer error"] [error="[ddl:8224]get zero backfill job"]
[2023/02/06 11:28:56.958 +00:00] [Info] [dist_backfilling.go:260] ["no backfill job, handle backfill task finished"]

4. What is your TiDB version? (Required)

Release Version: v6.6.0-alpha-379-g7b8038078e-dirty
Edition: Community
Git Commit Hash: 7b8038078e3e2ea71bf878c88b7320f513949e69
Git Branch: master