kvdb: move channeldb/kvdb to top level

contractcourt/briefcase_test.go

@@ -16,8 +16,8 @@ import (
 	"github.com/btcsuite/btcd/wire"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/channeldb"
-	"github.com/lightningnetwork/lnd/channeldb/kvdb"
 	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lntest/channels"
 	"github.com/lightningnetwork/lnd/lnwallet"
 )