cleanup(mixin): remove duplicated operations stub

[cuiy0006]

fix #14746

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This change is 

[codecov]

Codecov Report

Attention: Patch coverage is 91.57895% with 8 lines in your changes missing coverage. Please review.

Project coverage is 93.07%. Comparing base (03796d8) to head (eb1c11c).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
generator/internal/stub_factory_generator.cc	0.00%	3 Missing ⚠️
generator/internal/stub_generator.cc	0.00%	3 Missing ⚠️
...ration_tests/golden/v1/internal/request_id_stub.cc	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14838   +/-   ##
=======================================
  Coverage   93.07%   93.07%           
=======================================
  Files        2319     2319           
  Lines      209023   209035   +12     
=======================================
+ Hits       194538   194552   +14     
+ Misses      14485    14483    -2     

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[scotthart]

Reviewed 533 of 533 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @cuiy0006)