itest: Sync nodes to chain during singleHop tests

This ensures the Carol and Dave nodes created in the single_hop series
of tests are synced to the latest chain tip generated by the miner
before creating the route that will eventually be used for payments.

This prevents a flake during CI tests where slow processing of blocks by
Carol could cause the generated route to have a final CLTV delta too
short for Dave to accept.

While at it, we switch the test to use the default CLTV delta provided
by QueryRoutes which is now the global default CLTV.

lntest/itest/lnd_test.go

@@ -5381,14 +5381,23 @@ func testSingleHopSendToRouteCase(net *lntest.NetworkHarness, t *harnessTest,
 		payAddrs = append(payAddrs, resp.PaymentAddr)
 	}
 
-	// Query for routes to pay from Carol to Dave.
-	// We set FinalCltvDelta to 40 since by default QueryRoutes returns
-	// the last hop with a final cltv delta of 9 where as the default in
-	// htlcswitch is 40.
+	// Assert Carol and Dave are synced to the chain before proceeding, to
+	// ensure the queried route will have a valid final CLTV once the HTLC
+	// reaches Dave.
+	_, minerHeight, err := net.Miner.Node.GetBestBlock()
+	if err != nil {
+		t.Fatalf("unable to get best height: %v", err)
+	}
+	ctxt, cancel := context.WithTimeout(ctxb, defaultTimeout)
+	defer cancel()
+	require.NoError(t.t, waitForNodeBlockHeight(ctxt, carol, minerHeight))
+	require.NoError(t.t, waitForNodeBlockHeight(ctxt, dave, minerHeight))
+
+	// Query for routes to pay from Carol to Dave using the default CLTV
+	// config.
 	routesReq := &lnrpc.QueryRoutesRequest{
-		PubKey:         dave.PubKeyStr,
-		Amt:            paymentAmtSat,
-		FinalCltvDelta: lnd.DefaultBitcoinTimeLockDelta,
+		PubKey: dave.PubKeyStr,
+		Amt:    paymentAmtSat,
 	}
 	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
 	routes, err := carol.QueryRoutes(ctxt, routesReq)