examples/proxy: free cd[1] stat buckets in handle_close

When extended stats are enabled (-x), the per-connection setup allocates
rcv_bucket and snd_bucket for both directions, c->cd[0] and c->cd[1].
handle_close() only frees the cd[0] pair, so the two cd[1] arrays leak on
every connection teardown. Free them too, mirroring the cd[0] cleanup.

Signed-off-by: rootvector2 <dxbnaveed.k@gmail.com>