Removed check_program functions. Supporting these requires knowledge of CFF vs CFF2 state, whci is leads to wide-spread diffuse changes. Also, not needed - the endchar/return opcodes are removed when compiling for CFF2.
Removed CFF2Subr class. This was used for CFF2 CharStrings, and allowed avoiding referencing the width fields. I worked around this by providing dummy values for the Private.nominalWidthX and defaultWidthX.
Added a public method PrivateDict.in_cff2.