askrene: remove struct flow probability member.

Simply calculate it when we need it, which means we don't have to keep it
up-to-date as we tweak the flow.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

plugins/askrene/askrene.c

@@ -380,8 +380,7 @@ static const char *get_routes(const tal_t *ctx,
 		u32 delay;
 
 		(*routes)[i] = r = tal(*routes, struct route);
-		/* FIXME: flow_probability doesn't take into account other flows! */
-		r->success_prob = flows[i]->success_prob;
+		r->success_prob = flow_probability(flows[i], rq);
 		r->hops = tal_arr(r, struct route_hop, tal_count(flows[i]->path));
 
 		/* Fill in backwards to calc amount and delay */

plugins/askrene/flow.h

@@ -13,8 +13,7 @@ struct flow {
 	const struct gossmap_chan **path;
 	/* The directions to traverse. */
 	int *dirs;
-	/* Amounts for this flow (fees mean this shrinks across path). */
-	double success_prob;
+	/* Amount delivered */
 	struct amount_msat amount;
 };
 

plugins/askrene/mcf.c

@@ -1276,8 +1276,6 @@ get_flow_paths(const tal_t *ctx,
 			excess = amount_msat(0);
 			fp->amount = delivered;
 
-			fp->success_prob = flow_probability(fp, rq);
-
 			// add fp to flows
 			tal_arr_expand(&flows, fp);
 		}