kvdb: move channeldb/kvdb to top level

channeldb/migration16/migration.go

@@ -7,7 +7,7 @@ import (
 	"fmt"
 
 	"github.com/btcsuite/btcd/wire"
-	"github.com/lightningnetwork/lnd/channeldb/kvdb"
+	"github.com/lightningnetwork/lnd/kvdb"
 )
 
 var (

channeldb/migration16/migration_test.go

@@ -4,8 +4,8 @@ import (
 	"encoding/hex"
 	"testing"
 
-	"github.com/lightningnetwork/lnd/channeldb/kvdb"
 	"github.com/lightningnetwork/lnd/channeldb/migtest"
+	"github.com/lightningnetwork/lnd/kvdb"
 )
 
 var (