importinto: remove useless code and add test

[D3Hunter]

What problem does this PR solve?

Issue Number: ref #42930

Problem Summary:

What is changed and how it works?

lastInsertID is introduced when extending LOAD DATA, but now it's not used. add ut for precheck, it's covered by integration test only previously.

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

[tiprow]

Hi @D3Hunter. Thanks for your PR.

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[D3Hunter]

/ok-to-test

[codecov]

Codecov Report

Merging #46413 (d65610b) into master (3190885) will decrease coverage by 0.4838%.
Report is 17 commits behind head on master.
The diff coverage is 0.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #46413        +/-   ##
================================================
- Coverage   73.4100%   72.9262%   -0.4838%     
================================================
  Files          1292       1317        +25     
  Lines        393585     401877      +8292     
================================================
+ Hits         288931     293074      +4143     
- Misses        86282      90346      +4064     
- Partials      18372      18457        +85     

Flag	Coverage Δ
integration	25.8468% <0.0000%> (?)
unit	73.6019% <0.0000%> (+0.1919%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	85.0633% <ø> (ø)
br	47.9979% <ø> (-4.3605%)	⬇️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, lance6716

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-25 05:41:39.314658307 +0000 UTC m=+1473663.863674280: ☑️ agreed by lance6716.
• 2023-08-25 16:45:36.693200682 +0000 UTC m=+1513501.242216669: ☑️ agreed by hawkingrei.

[hawkingrei]

/retest