periodic: Move 320.whatis to the mandoc package

This periodic script only makes sense if mandoc is installed, so move
it to the mandoc package like other periodic scripts.

/usr/libexec/makewhatis.local only exists for the enjoyment of this
script, and doesn't work without mandoc installed, so move that as
well.

This change moves files between packages so, until we have a proper
policy on how to handle this in release/stable branches, it should
not be MFC'd.

MFC after:	never
Reviewed by:	ziaee, manu
Sponsored by:	https://www.patreon.com/bsdivy
Differential Revision:	https://reviews.freebsd.org/D53609

libexec/makewhatis.local/Makefile

@@ -1,3 +1,4 @@
+PACKAGE=	mandoc
 SCRIPTS=	makewhatis.local.sh
 MAN=		makewhatis.local.8
 SCRIPTSDIR=	${LIBEXECDIR}

usr.sbin/periodic/etc/weekly/Makefile

@@ -8,12 +8,11 @@ CONFS=	340.noid \
 
 # NB: keep these sorted by MK_* knobs
 
-.if ${MK_LOCATE} != "no"
-CONFS+=	310.locate
-.endif
+CONFGROUPS.${MK_LOCATE}+=	LOCATE
+LOCATE=	310.locate
 
-.if ${MK_MAN_UTILS} != "no"
-CONFS+=	320.whatis
-.endif
+CONFGROUPS.${MK_MAN_UTILS}+=	WHATIS
+WHATISPACKAGE=			mandoc
+WHATIS=	320.whatis
 
 .include <bsd.prog.mk>