fix: add additional and remove unused error const

[adrums86]

Description

Add and remove some error constants specific to videojs-contrib-eme errors.

Specific Changes proposed

Remove the keysystem specific errors as the keysystem is now passed as error metadata and add errors for remove and load calls on the MediaKeySession

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.71%. Comparing base (2f1cc6c) to head (ad3bdbb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8656   +/-   ##
=======================================
  Coverage   82.71%   82.71%           
=======================================
  Files         113      113           
  Lines        7636     7636           
  Branches     1835     1835           
=======================================
  Hits         6316     6316           
  Misses       1320     1320           

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