multi: only allow specifying towers to TowerClient through RPC

With the introduction of the WatchtowerClient RPC subserver, the lnd
configuration flag to specify private watchtowers for the client is no
longer needed and can lead to confusion upon users. Therefore, we remove
the flag completely, and only rely on the watchtower client being active
through a new --wtclient.active flag.

lntest/itest/lnd_test.go

@@ -35,6 +35,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc/invoicesrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/watchtowerrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/wtclientrpc"
 	"github.com/lightningnetwork/lnd/lntest"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
@@ -7708,22 +7709,27 @@ func testRevokedCloseRetributionAltruistWatchtower(net *lntest.NetworkHarness,
 			externalIP, willyInfo.Uris[0])
 	}
 
-	// Construct a URI from listening port and public key, since aren't
-	// actually connecting remotely.
-	willyTowerURI := fmt.Sprintf("%x@%s", willyInfo.Pubkey, listener)
-
 	// Dave will be the breached party. We set --nolisten to ensure Carol
 	// won't be able to connect to him and trigger the channel data
 	// protection logic automatically.
 	dave, err := net.NewNode("Dave", []string{
 		"--nolisten",
-		"--wtclient.private-tower-uris=" + willyTowerURI,
+		"--wtclient.active",
 	})
 	if err != nil {
 		t.Fatalf("unable to create new node: %v", err)
 	}
 	defer shutdownAndAssert(net, t, dave)
 
+	ctxt, _ = context.WithTimeout(ctxb, defaultTimeout)
+	addTowerReq := &wtclientrpc.AddTowerRequest{
+		Pubkey:  willyInfo.Pubkey,
+		Address: listener,
+	}
+	if _, err := dave.WatchtowerClient.AddTower(ctxt, addTowerReq); err != nil {
+		t.Fatalf("unable to add willy's watchtower: %v", err)
+	}
+
 	// We must let Dave have an open channel before she can send a node
 	// announcement, so we open a channel with Carol,
 	if err := net.ConnectNodes(ctxb, dave, carol); err != nil {