textproc/groff: Fix build/packaging with URWFONTS disabled

With URWFONTS disabled, the groff build fails:

pdfroff: installation problem: cannot find GhostScript interpreter

• FATAL INSTALLATION ERROR ***

'pdfroff' requires a GhostScript interpreter to convert PostScript to PDF.
Since you do not appear to have one installed, 'pdfroff' connot continue.

This change provides configure with a more explicit argument to disable
ghostscript, vs the CONFIGURE_ENV method [1] introduced in ports 499077
after ports r499075 introduced the option.

Update pkg-plist to mark files not conditional on this option.

PR: 237615
Submitted by: <fullermd over-yonder net> [1]
Approved by: portmgr (blanket: build fix, just fix it)
MFH: no (not affected)