Remove unused dead code in BamlMapTable / XamlTypeMapper

[h3xds1nz]

This follows #10636 which removes the uncalled Initialize method (here I just remove one of the called methods inside).

Description

Removes unused code since NetFX4 in BamlMapTable / XamlTypeMapper.
They're independent of each other actually but the removal makes sense to do together.

Customer Impact

Smaller assembly size, cleaner codebase for developers.

Regression

No.

Testing

Local build.

Risk

Low, unused dead code.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.98889%. Comparing base (57fe8ac) to head (308ae72).
Report is 10 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main     #10881          +/-   ##
===================================================
- Coverage   13.48885%   2.98889%   -10.49996%     
===================================================
  Files           3317       3319           +2     
  Lines         664749     664729          -20     
  Branches       74643      74649           +6     
===================================================
- Hits           89667      19868       -69799     
- Misses        572488     644680       +72192     
+ Partials        2594        181        -2413     

Flag	Coverage Δ
Debug	2.98889% <ø> (-10.49996%)	⬇️

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