gnu: Use ghostscript over ghostscript-gs.

gnu: Use ghostscript over ghostscript-gs.

* gnu/packages/engineering.scm (fastcap)[native-inputs],
gnu/packages/lout.scm (lout)[native-inputs],
gnu/packages/ocaml.scm (unison)[native-inputs],
gnu/packages/plotutils.scm (asymptote)[native-inputs],
gnu/packages/skribilo.scm (skribilo)[native-inputs]: Remove
ghostscript-gs.
* gnu/packages/gv.scm (gv)[propagated-inputs],
gnu/packages/music.scm (lilypond)[inputs],
gnu/packages/scheme.scm (chez-scheme)[native-inputs]: Use
ghostscript over ghostscript-gs.