libcupsfilters: For ghostscript() require GS 9.56.0

libcupsfilters: For ghostscript() require GS 9.56.0

Removed the conditionals for the presence or absemse of the
"appleraster" output device in Ghostscript (version 9.56.0 and
newer). We already require that the "pclm" device is there (GS version
9.55.0 and newer). So we remove the conditionals now and simply
require Ghostscript 9.56.0.