[Cleanup] Remove legacy metrics protocol check in DefaultMetricsServiceExporter

[LI123456mo]

*Resolved the TODO in DefaultMetricsServiceExporter. Since the new metrics mechanism is ready, I removed the manual protocol checks for Prometheus and Default. This simplifies the initialization logic and removes unused constants.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 58.75%. Comparing base (a3a35b5) to head (e4e9d86).

Files with missing lines	Patch %	Lines
...o/config/deploy/DefaultMetricsServiceExporter.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #15927      +/-   ##
============================================
- Coverage     60.74%   58.75%   -2.00%     
+ Complexity    11702       15   -11687     
============================================
  Files          1938     1938              
  Lines         88694    88689       -5     
  Branches      13387    13387              
============================================
- Hits          53879    52105    -1774     
- Misses        29291    30928    +1637     
- Partials       5524     5656     +132     

Flag	Coverage Δ
integration-tests-java21	?
integration-tests-java8	?
samples-tests-java21	?
samples-tests-java8	?
unit-tests-java11	59.00% <66.66%> (-0.05%)	⬇️
unit-tests-java17	58.48% <66.66%> (-0.05%)	⬇️
unit-tests-java21	58.48% <66.66%> (-0.04%)	⬇️
unit-tests-java25	58.40% <66.66%> (-0.07%)	⬇️
unit-tests-java8	58.99% <66.66%> (-0.05%)	⬇️

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