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 13.47840%. Comparing base (b7f5416) to head (fb8ef94).
Report is 2 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10666         +/-   ##
===================================================
- Coverage   13.71795%   13.47840%   -0.23955%     
===================================================
  Files           3317        3316          -1     
  Lines         665537      665435        -102     
  Branches       74666       74655         -11     
===================================================
- Hits           91298       89690       -1608     
- Misses        571542      573145       +1603     
+ Partials        2697        2600         -97     

Flag	Coverage Δ
Debug	13.47840% <ø> (-0.23955%)	⬇️

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[siagupta0202]

LGTM, @h3xds1nz can you resolve the merge conflicts?

[h3xds1nz]

@siagupta0202 Done :)

[siagupta0202]

@h3xds1nz Thank you so much for your contributions!

[h3xds1nz]

@siagupta0202 Thanks you :) Now we just need to process #10667 haha.