Removed specialization for while nodes on non-block receivers

This is not part of SOM. #whileTrue: and #whileFalse: are only supported on the Block class.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Refactor superclass parsing to be an explicit method in the parser.

Signed-off-by: Stefan Marr <git@stefan-marr.de>