Remove documentation references to MEF

[JamieMagee]

We migrated away from MEF to dependency injection back in #412. This PR removes references to MEF that still remain in documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.3%. Comparing base (9442735) to head (9579ce6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1525   +/-   ##
=====================================
  Coverage   90.3%   90.3%           
=====================================
  Files        418     418           
  Lines      35275   35275           
  Branches    2188    2188           
=====================================
+ Hits       31881   31882    +1     
  Misses      2951    2951           
+ Partials     443     442    -1     

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