f - inline fresh selection in discard_unique_contribution test

This test specifically requires fresh inputs across RBF rounds (it
clears the wallet between rounds and asserts the inputs differ).
Inline the splice_channel + funding_contributed flow with
without_prior_contribution rather than using a helper, since this
is the only call site that needs that behavior.

Author: jkczyz

lightning/src/ln/splicing_tests.rs

@@ -4743,8 +4743,18 @@ fn test_splice_rbf_discard_unique_contribution() {
 
 	// Round 1: RBF with fresh UTXOs, splice-in only (no splice-out output).
 	let rbf_feerate = FeeRate::from_sat_per_kwu(FEERATE_FLOOR_SATS_PER_KW as u64 + 25);
-	let funding_contribution =
-		do_initiate_rbf_splice_in(&nodes[0], &nodes[1], channel_id, added_value, rbf_feerate);
+	let funding_template = nodes[0].node.splice_channel(&channel_id, &node_id_1).unwrap();
+	let wallet = WalletSync::new(Arc::clone(&nodes[0].wallet_source), nodes[0].logger);
+	let funding_contribution = funding_template
+		.without_prior_contribution(rbf_feerate, FeeRate::MAX)
+		.with_coin_selection_source_sync(&wallet)
+		.add_value(added_value)
+		.build()
+		.unwrap();
+	nodes[0]
+		.node
+		.funding_contributed(&channel_id, &node_id_1, funding_contribution.clone(), None)
+		.unwrap();
 	let round_1_inputs: Vec<_> = funding_contribution.contributed_inputs().collect();
 	assert_ne!(round_0_inputs, round_1_inputs, "Rounds must use different UTXOs");