graph: remove DB interface

graph/builder.go

@@ -55,7 +55,7 @@ type Config struct {
 
 	// Graph is the channel graph that the ChannelRouter will use to gather
 	// metrics from and also to carry out path finding queries.
-	Graph DB
+	Graph *graphdb.ChannelGraph
 
 	// Chain is the router's source to the most up-to-date blockchain data.
 	// All incoming advertised channels will be checked against the chain