further clean up OS differences in makefiles

No need for if() logic.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

doc/Makefile

@@ -1,27 +1,11 @@
 DIR=	${DOCDIR}/openrc
+SRCS=	net.example.in
 INC=	net.example
 
 MK=	../mk
 include ${MK}/os.mk
 
-ifeq (${OS},FreeBSD)
-SRCS+=		net.example.in
-
-.SUFFIXES:	.BSD.in
-.BSD.in:
+${SFX}:
 	${CP} $< $@
-else ifeq (${OS},Linux)
-SRCS+=		net.example.in
-
-.SUFFIXES:	.Linux.in
-.Linux.in:
-	${CP} $< $@
-else ifeq (${OS},NetBSD)
-SRCS+=		net.example.in
-
-.SUFFIXES:	.BSD.in
-.BSD.in:
-	${CP} $< $@
-endif
 
 include ${MK}/scripts.mk