CLEANUP: stream-int:  Remove unused SI functions

Some stream-interface's functions are now unused and can safely be removed.
diff --git a/include/haproxy/stream_interface.h b/include/haproxy/stream_interface.h
index 655e30a..3ffc3f4 100644
--- a/include/haproxy/stream_interface.h
+++ b/include/haproxy/stream_interface.h
@@ -49,56 +49,6 @@
 int cs_conn_send(struct conn_stream *cs);
 int cs_conn_process(struct conn_stream *cs);
 
-/* returns the channel which receives data from this stream interface (input channel) */
-static inline struct channel *si_ic(struct stream_interface *si)
-{
-	struct stream *strm = __cs_strm(si->cs);
-
-	return ((si->flags & SI_FL_ISBACK) ? &(strm->res) : &(strm->req));
-}
-
-/* returns the channel which feeds data to this stream interface (output channel) */
-static inline struct channel *si_oc(struct stream_interface *si)
-{
-	struct stream *strm = __cs_strm(si->cs);
-
-	return ((si->flags & SI_FL_ISBACK) ? &(strm->req) : &(strm->res));
-}
-
-/* returns the buffer which receives data from this stream interface (input channel's buffer) */
-static inline struct buffer *si_ib(struct stream_interface *si)
-{
-	return &si_ic(si)->buf;
-}
-
-/* returns the buffer which feeds data to this stream interface (output channel's buffer) */
-static inline struct buffer *si_ob(struct stream_interface *si)
-{
-	return &si_oc(si)->buf;
-}
-
-/* returns the stream associated to a stream interface */
-static inline struct stream *si_strm(struct stream_interface *si)
-{
-	return __cs_strm(si->cs);
-}
-
-/* returns the task associated to this stream interface */
-static inline struct task *si_task(struct stream_interface *si)
-{
-	struct stream *strm = __cs_strm(si->cs);
-
-	return strm->task;
-}
-
-/* returns the stream interface on the other side. Used during forwarding. */
-static inline struct stream_interface *si_opposite(struct stream_interface *si)
-{
-	struct stream *strm = __cs_strm(si->cs);
-
-	return ((si->flags & SI_FL_ISBACK) ? strm->csf->si : strm->csb->si);
-}
-
 /* initializes a stream interface and create the event
  * tasklet.
  */