ddl: remove redundant backfill metric counting

[tangenta]

What problem does this PR solve?

Problem Summary:

The backfill total counter has been updated in

tidb/ddl/index.go

Line 1649 in 0f7bb0a

w.metricCounter.Add(float64(cnt))

Let's remove the incorrect counting here.

What is changed and how it works?

After this PR:

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• hawkingrei
• wjhuang2016

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[hawkingrei]

/retest

[zimulala]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 060e9c6