chore(developer): refactor kmcmplib interfaces

Relates to #8493.

* Removes kmcmplib calls from kmcmpdll (now that we have kmc)
* Removes old kmcmp_CompileKeyboardFile and
  kmcmp_CompileKeyboardFileToBuffer functions in preference for a much
  cleaner kmcmp_CompileKeyboard function
* Removes json validation helper from kmcmplib (we'll use js-native
  json schema validation instead)

This change means that we no longer need to keep compfile.h consistent
between kmcmplib and kmcmpdll. This will simplify upcoming refactoring
of kmcmplib.

kmcmplib no longer writes files, but it does still read them. The next
refactor will move file load responsibility into the caller.