CLEANUP: applet: rename struct si_applet to applet

Since this one does not depend on stream_interface anymore, remove the
"si_" prefix.
diff --git a/include/proto/stream_interface.h b/include/proto/stream_interface.h
index 2645961..036a4e1 100644
--- a/include/proto/stream_interface.h
+++ b/include/proto/stream_interface.h
@@ -44,7 +44,7 @@
 extern struct data_cb si_conn_cb;
 extern struct data_cb si_idle_conn_cb;
 
-struct appctx *stream_int_register_handler(struct stream_interface *si, struct si_applet *app);
+struct appctx *stream_int_register_handler(struct stream_interface *si, struct applet *app);
 void stream_int_unregister_handler(struct stream_interface *si);
 
 /* returns the channel which receives data from this stream interface (input channel) */
@@ -274,7 +274,7 @@
  * and returned. NULL may be returned upon memory shortage. Applet <applet>
  * is assigned to the appctx, but it may be NULL.
  */
-static inline struct appctx *si_alloc_appctx(struct stream_interface *si, struct si_applet *applet)
+static inline struct appctx *si_alloc_appctx(struct stream_interface *si, struct applet *applet)
 {
 	struct appctx *appctx;