dtrace: Remove $FreeBSD$ from genmakefiles.sh.

$FreeBSD$ is gone in head, so this should be removed as well.

Reviewed by:	imp
Differential Revision:	https://reviews.freebsd.org/D41595

cddl/usr.sbin/dtrace/tests/tools/genmakefiles.sh

@@ -59,8 +59,6 @@ WITH_CTF=YES
 
     local makefile=$(mktemp)
     cat <<__EOF__ > $makefile
-# \$FreeBSD$
-
 #
 # This Makefile was generated by \$srcdir${ORIGINDIR#${TOPDIR}}/genmakefiles.sh.
 #