Tmpfiles: create and delete entries once in the boot runlevel.

Initially, we were creating tmpfiles entries in the sysinit runlevel and
again in the boot runlevel. Systemd runs the --create and --remove
options in one service called systemd-tmpfiles-setup after the local
file systems are mounted. Now we have a service called tmpfiles.setup
which emulates this.

This also closes the bug mentioned below, since we were originally
writing to files that were on read-only file systems and that were not
available.

Reported-by: <devurandom@gmx.net>
X-Gentoo-Bug: 439012
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=439012

conf.d/Makefile

@@ -1,5 +1,5 @@
 DIR=	${CONFDIR}
-CONF=	bootmisc fsck hostname localmount netmount urandom tmpfilesd \
+CONF=	bootmisc fsck hostname localmount netmount urandom tmpfiles \
 		${CONF-${OS}}
 
 ifeq (${MKNET},)