watchtower: remove dev tag from unit test files

Several watchtower unit tests were not being executed by make unit since
they require the dev tag to be passed in. All tests still pass.

watchtower/lookout/justice_descriptor_test.go

@@ -1,5 +1,3 @@
-// +build dev
-
 package lookout_test
 
 import (

watchtower/lookout/lookout_test.go

@@ -1,5 +1,3 @@
-// +build dev
-
 package lookout_test
 
 import (

watchtower/lookout/mock.go

@@ -1,5 +1,3 @@
-// +build dev
-
 package lookout
 
 import (

watchtower/wtclient/client_test.go

@@ -1,5 +1,3 @@
-// +build dev
-
 package wtclient_test
 
 import (
@@ -24,6 +22,7 @@ import (
 	"github.com/lightningnetwork/lnd/watchtower/wtmock"
 	"github.com/lightningnetwork/lnd/watchtower/wtpolicy"
 	"github.com/lightningnetwork/lnd/watchtower/wtserver"
+	"github.com/stretchr/testify/require"
 )
 
 const (
@@ -1457,7 +1456,8 @@ var clientTests = []clientTest{
 			// Re-add the tower. We prevent the tower from acking
 			// session creation to ensure the inactive sessions are
 			// not used.
-			h.server.Stop()
+			err := h.server.Stop()
+			require.Nil(h.t, err)
 			h.serverCfg.NoAckCreateSession = true
 			h.startServer()
 			h.addTower(h.serverAddr)
@@ -1466,7 +1466,8 @@ var clientTests = []clientTest{
 			// Finally, allow the tower to ack session creation,
 			// allowing the state updates to be sent through the new
 			// session.
-			h.server.Stop()
+			err = h.server.Stop()
+			require.Nil(h.t, err)
 			h.serverCfg.NoAckCreateSession = false
 			h.startServer()
 			h.waitServerUpdates(hints[numUpdates/2:], 5*time.Second)