Remove WinRT ReflectionHelper dead code (compiled, not used)

[h3xds1nz]

Description

Removes the ReflectionHelper static class from the WindowsRuntime namespace. We do use ReflectionHelper, but that's one put in System.Windows.Markup that's used pretty much by all libraries and is a different from this impl.

This one popped up in netfx4 during the inclusion of WinRT into the codebase but wasn't used.

Customer Impact

Cleaner codebase for developers.

Regression

No.

Testing

Local build.

Risk

None, unused dead code.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 11.41176%. Comparing base (0d19d68) to head (8221af4).
Report is 6 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10666         +/-   ##
===================================================
+ Coverage   11.27425%   11.41176%   +0.13750%     
===================================================
  Files           3353        3352          -1     
  Lines         668062      667960        -102     
  Branches       74980       74969         -11     
===================================================
+ Hits           75319       76226        +907     
+ Misses        591489      590383       -1106     
- Partials        1254        1351         +97     

Flag	Coverage Δ
Debug	11.41176% <ø> (+0.13750%)	⬆️

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