*: remove the variable txn_scope

[ekexium]

What problem does this PR solve?

Issue Number: ref #58838

Problem Summary:

What changed and how does it work?

Remove the variable txn_scope

Check List

Tests

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

  • I checked and no code files have been changed.

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

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[tiprow]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.8826%. Comparing base (b22555b) to head (3e8e5c0).
Report is 6 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58839        +/-   ##
================================================
+ Coverage   73.1419%   74.8826%   +1.7407%     
================================================
  Files          1677       1722        +45     
  Lines        463823     473171      +9348     
================================================
+ Hits         339249     354323     +15074     
+ Misses       103716      96536      -7180     
- Partials      20858      22312      +1454     

Flag	Coverage Δ
integration	48.6687% <ø> (?)
unit	72.2756% <ø> (-0.0656%)	⬇️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	61.6314% <ø> (+15.9134%)	⬆️