etcd: remove (unused) etcd root bucket prefix

This commit removes the unused prefix from the etcd backend config as
etcd key space separation in LND is implemented by using namespaces
instead.

lnd.go

@@ -1455,9 +1455,7 @@ func initializeDatabases(ctx context.Context,
 
 	startOpenTime := time.Now()
 
-	databaseBackends, err := cfg.DB.GetBackends(
-		ctx, cfg.localDatabaseDir(), cfg.networkName(),
-	)
+	databaseBackends, err := cfg.DB.GetBackends(ctx, cfg.localDatabaseDir())
 	if err != nil {
 		return nil, nil, nil, fmt.Errorf("unable to obtain database "+
 			"backends: %v", err)