Stop setting btrfs_noversion build tag

c/storage no longer uses this tag after
https://github.com/containers/storage/pull/2308.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

hack/btrfs_tag.sh

@@ -1,7 +0,0 @@
-#!/usr/bin/env bash
-${CPP:-${CC:-cc} -E} ${CPPFLAGS} - > /dev/null 2> /dev/null << EOF
-#include <btrfs/version.h>
-EOF
-if test $? -ne 0 ; then
-	echo btrfs_noversion
-fi