rc-functions.sh: Remove addon support

This is an old relic from Gentoo baselayout-1.x which should not be used
any longer.

sh/Makefile

@@ -1,6 +1,6 @@
 DIR=	${LIBEXECDIR}/sh
 SRCS=	init.sh.in functions.sh.in gendepends.sh.in \
-	openrc-run.sh.in rc-functions.sh.in ${SRCS-${OS}}
+	openrc-run.sh.in ${SRCS-${OS}}
 INC=	rc-mount.sh functions.sh rc-functions.sh runit.sh s6.sh \
 		start-stop-daemon.sh supervise-daemon.sh
 BIN=	gendepends.sh init.sh openrc-run.sh ${BIN-${OS}}