graph: remove one context.TODO

By threading a context through to the Builder's ForAllOutgoingChannels
method.

graph/interfaces.go

@@ -70,8 +70,9 @@ type ChannelGraphSource interface {
 	// ForAllOutgoingChannels is used to iterate over all channels
 	// emanating from the "source" node which is the center of the
 	// star-graph.
-	ForAllOutgoingChannels(cb func(c *models.ChannelEdgeInfo,
-		e *models.ChannelEdgePolicy) error) error
+	ForAllOutgoingChannels(ctx context.Context,
+		cb func(c *models.ChannelEdgeInfo,
+			e *models.ChannelEdgePolicy) error) error
 
 	// CurrentBlockHeight returns the block height from POV of the router
 	// subsystem.