raftstore-v2: not update modification index for delete range (#14905)

[ti-chi-bot]

This is an automated cherry-pick of #14905

What is changed and how it works?

Issue Number: Close #14904

What's Changed:

not update modification index for delete range 

If key range are matched well with sst files, delete range may not produce entries in memtable. It means it is possible that the memtable is empty after delete range for default cf for instance, and there's no further write/delete for default cf, last_modified will never equal to last_flushed for this cf. So, admin flushed index will never be progressed.

As delete range is an usafe operation and cannot be rollbacked to replay, so it's better to not modify the modification index for delete range operation.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Release note

None

[ti-chi-bot]

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[ti-chi-bot]

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