Remove `groff' from USES.

It was recently killed in the base system and consumers have to use
`textproc/groff' port now, which is a real PITA: it pulls in some
obscure dependencies like `print/psutils', `graphics/netpbm', but
most importantly, `ghostscript' (unconditionally), which is a huge
abomination of its own, pulling another round of dependencies, some
of which are as crazy as `graphics/svgalib' (sic).  Trying to reset
all offered knobs to `off' results in unbuildable package.

Pass NROFF as mere `echo' and be done with it.  Generated manpages
remain identical.

x11-toolkits/fltk/Makefile

@@ -15,12 +15,13 @@ LICENSE_FILE=	${WRKSRC}/COPYING
 
 LIB_DEPENDS=	libpng.so:graphics/png
 
-USES=		groff jpeg localbase pkgconfig
+USES=		jpeg localbase pkgconfig
 USE_XORG=	x11 xcursor xext xfixes xft xinerama
 USE_GL=		glu
 USE_LDCONFIG=	yes
 GNU_CONFIGURE=	yes
 CONFIGURE_ARGS=	--enable-shared
+CONFIGURE_ENV=	NROFF=echo
 
 WRKSRC=		${WRKDIR}/${PORTNAME}-${PORTVERSION}
 

x11-toolkits/fltk/files/patch-configure

@@ -1,5 +1,14 @@
 --- configure.orig	2016-11-11 16:04:30 UTC
 +++ configure
+@@ -4193,7 +4193,7 @@ if ${ac_cv_path_NROFF+:} false; then :
+   $as_echo_n "(cached) " >&6
+ else
+   case $NROFF in
+-  [\\/]* | ?:[\\/]*)
++  [\\/]* | ?:[\\/]* | echo)
+   ac_cv_path_NROFF="$NROFF" # Let the user override the test with a path.
+   ;;
+   *)
 @@ -7408,7 +7408,7 @@ $as_echo "$as_me: WARNING: Ignoring libraries \"$X_PRE
  	LIBS="$LIBS -lX11 $X_EXTRA_LIBS"
  	CFLAGS="$CFLAGS $X_CFLAGS"