expression: fix unstable test TestExprOnlyPushDownToFlash

[LittleFall]

What problem does this PR solve?

Issue Number: close #25584, partially #25899

Problem Summary: see #25584 (comment)

What is changed and how it works?

What's Changed: remove functions about blacklist here.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn: no need
• Need to cherry-pick to the release branch: no need

Check List

Tests

• Integration test
• Manual test (add detailed scripts or steps below)

Side effects

• Performance regression
  • Consumes more CPU
  • Consumes more MEM
• Breaking backward compatibility

Release note

• No release note

[LittleFall]

/run-unit-test

[LittleFall]

/run-unit-test

[LittleFall]

/run-unit-test

[LittleFall]

/run-unit-test

[LittleFall]

/run-unit-test

[LittleFall]

/run-unit-test

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[fzhedu]

/LGTM

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[LittleFall]

/merge

[ti-chi-bot]

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

Commit hash: 4ed2915

[LittleFall]

/merge

[ti-chi-bot]

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

Commit hash: 2b6e91e

[LittleFall]

The result of the attempt shows: test suite with bootstrap such as testIntegrationSuiteBase will initialize the blacklist, and will not eliminate it after teardown.

If the suite tested of TestExprOnlyPushDownToFlash is set to serial, then this error will inevitably occur. The minimum recurrence is: go test -v ./expression/... -check.f "TestExprPushdownBlacklist|TestExprOnlyPushDownToFlash".

Another solution is to manually eliminate the blacklist when every suite is tearing down.

	tk := testkit.NewTestKit(c, s.store)
	tk.MustExec("use mysql")
	tk.MustExec("delete from expr_pushdown_blacklist")
	tk.MustExec("admin reload expr_pushdown_blacklist")

but it is too stupid.