[cleanup][test]delete invalid method in PrometheusMetricsTest

[guan46]

Motivation

I found we defined some methods, but does not used these.

Modifications

Remove the unnecessary method.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.51%. Comparing base (bbc6224) to head (3c2bf49).
Report is 552 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23218      +/-   ##
============================================
+ Coverage     73.57%   74.51%   +0.93%     
- Complexity    32624    33693    +1069     
============================================
  Files          1877     1922      +45     
  Lines        139502   144748    +5246     
  Branches      15299    15832     +533     
============================================
+ Hits         102638   107853    +5215     
+ Misses        28908    28637     -271     
- Partials       7956     8258     +302     

Flag	Coverage Δ
inttests	27.86% <ø> (+3.28%)	⬆️
systests	24.68% <ø> (+0.36%)	⬆️
unittests	73.86% <ø> (+1.01%)	⬆️

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see 536 files with indirect coverage changes