reinstall the roff(7) manpage

When we had both groff and mandoc in base, we decided to keep the roff(7)
manpage from groff. when remoing groff, we forgot to install the mandoc version
instead.

This fixes it.

Reported by:	trasz
MFC after:	1 week

ObsoleteFiles.inc

@@ -1070,7 +1070,6 @@ OLD_FILES+=usr/share/man/man7/mm.7.gz
 OLD_FILES+=usr/share/man/man7/mmse.7.gz
 OLD_FILES+=usr/share/man/man7/ms.7.gz
 OLD_FILES+=usr/share/man/man7/orig_me.7.gz
-OLD_FILES+=usr/share/man/man7/roff.7.gz
 OLD_FILES+=usr/share/me/acm.me
 OLD_FILES+=usr/share/me/chars.me
 OLD_FILES+=usr/share/me/deltext.me

usr.bin/mandoc/Makefile

@@ -6,7 +6,7 @@ MDOCMLDIR=	${SRCTOP}/contrib/mdocml
 .PATH: ${MDOCMLDIR}
 
 PROG=	mandoc
-MAN=	mandoc.1 eqn.7 mandoc_char.7 tbl.7 man.7 mdoc.7 # roff.7
+MAN=	mandoc.1 eqn.7 mandoc_char.7 tbl.7 man.7 mdoc.7 roff.7
 MLINKS=	mandoc.1 mdocml.1
 .if ${MK_MAN_UTILS} != no
 MAN+=	apropos.1 makewhatis.8