Move libalias.conf to lib/libalias/libalias/

This leveages CONFS to handle the install.

Approved by:	re (blanket, pkgbase), bapt (mentor)
Differential Revision:	https://reviews.freebsd.org/D17218

etc/Makefile

@@ -15,7 +15,6 @@ SUBDIR+=sendmail
 BIN1=	\
 	group \
 	hosts.allow \
-	libalias.conf \
 	login.access \
 	phones \
 	rc.bsdextended \

lib/libalias/libalias/Makefile

@@ -2,6 +2,7 @@
 
 .PATH: ${SRCTOP}/sys/netinet/libalias
 
+CONFS=	libalias.conf
 PACKAGE=lib${LIB}
 LIB=	alias
 SHLIBDIR?= /lib