ctdb-build: Tweak hacking of rpcgen output

csbuild doesn't like the hack where variable buf is initialised to
itself to avoid an unused variable warning.  buf is unused so remove
it instead.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>

ctdb/wscript

@@ -634,7 +634,7 @@ def build(bld):
                         target='utils/smnotify/smnotify.h',
                         rule='rpcgen -h ${SRC} > ${TGT}')
 
-    xdr_buf_hack = 'sed -e "s@^\([ \t]*register int32_t \*buf\);@\\1 = buf;@"'
+    xdr_buf_hack = 'grep -Fv "register int32_t *buf;"'
 
     bld.SAMBA_GENERATOR('ctdb-smnotify-x',
                         source='utils/smnotify/smnotify.x',