etcd: refactors to simplify etcd configuration

This refactor removes a redundancy where we had etcd configuration under
kvdb and kvdb/etcd packages.

lncfg/db.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/lightningnetwork/lnd/channeldb/kvdb"
+	"github.com/lightningnetwork/lnd/channeldb/kvdb/etcd"
 )
 
 const (
@@ -21,7 +22,7 @@ type DB struct {
 
 	BatchCommitInterval time.Duration `long:"batch-commit-interval" description:"The maximum duration the channel graph batch schedulers will wait before attempting to commit a batch of pending updates. This can be tradeoff database contenion for commit latency."`
 
-	Etcd *kvdb.EtcdConfig `group:"etcd" namespace:"etcd" description:"Etcd settings."`
+	Etcd *etcd.Config `group:"etcd" namespace:"etcd" description:"Etcd settings."`
 
 	Bolt *kvdb.BoltConfig `group:"bolt" namespace:"bolt" description:"Bolt settings."`
 }