MEDIUM: stream_interface: remove CAP_SPLTCP/CAP_SPLICE flags

These ones are implicitly handled by the connection's data layer, no need
to rely on them anymore and reaching them maintains undesired dependences
on stream-interface.
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index edc97d0..8b069c8 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -69,7 +69,7 @@
 	SI_FL_ERR        = 0x0002,  /* a non-recoverable error has occurred */
 	SI_FL_WAIT_ROOM  = 0x0004,  /* waiting for space to store incoming data */
 	SI_FL_WAIT_DATA  = 0x0008,  /* waiting for more data to send */
-	SI_FL_CAP_SPLTCP = 0x0010,  /* splicing possible from/to TCP */
+	/* unused          0x0010 */
 	SI_FL_DONT_WAKE  = 0x0020,  /* resync in progress, don't wake up */
 	SI_FL_INDEP_STR  = 0x0040,  /* independent streams = don't update rex on write */
 	SI_FL_NOLINGER   = 0x0080,  /* may close without lingering. One-shot. */
@@ -77,8 +77,6 @@
 	SI_FL_SRC_ADDR   = 0x1000,  /* get the source ip/port with getsockname */
 };
 
-#define SI_FL_CAP_SPLICE (SI_FL_CAP_SPLTCP)
-
 struct stream_interface;
 
 /* operations available on a stream-interface */