CLEANUP: connection: remove the unused conn_sock_shutw_pending()

This has never been used anywhere.
diff --git a/include/proto/connection.h b/include/proto/connection.h
index 3a31fa3..8c0301c 100644
--- a/include/proto/connection.h
+++ b/include/proto/connection.h
@@ -462,12 +462,6 @@
 	return (c->flags & CO_FL_SOCK_RD_SH) != 0;
 }
 
-/* detect data->sock shutw transition */
-static inline int conn_sock_shutw_pending(struct connection *c)
-{
-	return (c->flags & (CO_FL_DATA_WR_SH | CO_FL_SOCK_WR_SH)) == CO_FL_DATA_WR_SH;
-}
-
 /* prepares a connection to work with protocol <proto> and transport <xprt>.
  * The transport's context is initialized as well.
  */