src.opts.mk: Retire BSD_CPIO option

Prior to commit 6973701a00 ("1. Make the BSD version of cpio the
default [1]") GNU cpio was installed unconditionally.  The BSD_CPIO
option was added when we introduced the BSD licensed, libarchive-based
cpio, to support installation of GNU cpio, libarchive cpio, or both.

GNU cpio was removed long ago and there is no longer a need for this
option.  We can just install BSD cpio unconditionally.

Reviewed by:	des
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55467

usr.bin/Makefile

@@ -24,6 +24,7 @@ SUBDIR=	apply \
 	comm \
 	command \
 	compress \
+	cpio \
 	csplit \
 	ctlstat \
 	cut \
@@ -185,7 +186,6 @@ SUBDIR=	apply \
 SUBDIR.${MK_ACCT}+=	lastcomm
 SUBDIR.${MK_AT}+=	at
 SUBDIR.${MK_BLUETOOTH}+=	bluetooth
-SUBDIR.${MK_BSD_CPIO}+=	cpio
 SUBDIR.${MK_CALENDAR}+=	calendar
 .if ${MK_CLANG} != "no" || ${MK_LLVM_BINUTILS} != "no" || \
     ${MK_LLD} != "no" || ${MK_LLDB} != "no"