graph/db: remove GraphCacheNode interface

With the previous commit, the AddNode method was removed and since that
was the only method making use of the ForEachChannel on the
GraphCacheNode interface, we can remove that method. Since the only two
methods left just expose the node's pub key and features, it really is
not required anymore and so the entire thing can be removed along with
the implementation of it.

graph/db/graph_cache_test.go

@@ -5,7 +5,6 @@ import (
 	"testing"
 
 	"github.com/lightningnetwork/lnd/graph/db/models"
-	"github.com/lightningnetwork/lnd/kvdb"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/stretchr/testify/require"
@@ -25,39 +24,6 @@ var (
 	pubKey2, _ = route.NewVertexFromBytes(pubKey2Bytes)
 )
 
-type node struct {
-	pubKey   route.Vertex
-	features *lnwire.FeatureVector
-
-	edgeInfos   []*models.ChannelEdgeInfo
-	outPolicies []*models.ChannelEdgePolicy
-	inPolicies  []*models.ChannelEdgePolicy
-}
-
-func (n *node) PubKey() route.Vertex {
-	return n.pubKey
-}
-func (n *node) Features() *lnwire.FeatureVector {
-	return n.features
-}
-
-func (n *node) ForEachChannel(tx kvdb.RTx,
-	cb func(kvdb.RTx, *models.ChannelEdgeInfo, *models.ChannelEdgePolicy,
-		*models.ChannelEdgePolicy) error) error {
-
-	for idx := range n.edgeInfos {
-		err := cb(
-			tx, n.edgeInfos[idx], n.outPolicies[idx],
-			n.inPolicies[idx],
-		)
-		if err != nil {
-			return err
-		}
-	}
-
-	return nil
-}
-
 // TestGraphCacheAddNode tests that a channel going from node A to node B can be
 // cached correctly, independent of the direction we add the channel as.
 func TestGraphCacheAddNode(t *testing.T) {
@@ -85,12 +51,8 @@ func TestGraphCacheAddNode(t *testing.T) {
 			ChannelFlags: lnwire.ChanUpdateChanFlags(channelFlagB),
 			ToNode:       nodeA,
 		}
-		node := &node{
-			pubKey:   nodeA,
-			features: lnwire.EmptyFeatureVector(),
-		}
 		cache := NewGraphCache(10)
-		cache.AddNodeFeatures(node)
+		cache.AddNodeFeatures(nodeA, lnwire.EmptyFeatureVector())
 		cache.AddChannel(&models.ChannelEdgeInfo{
 			ChannelID: 1000,
 			// Those are direction independent!