lnrpc+routing: fix issues with missing data in unmarshallRoute

In this commit the dependency of unmarshallRoute on edge policies being
available is removed. Edge policies may be unknown and reported as nil.
SendToRoute does not need the policies, but it does need pubkeys of the
route hops. In this commit, unmarshallRoute is modified so that it
takes the pubkeys from edgeInfo instead of channelEdgePolicy.

In addition to this, the route structure is simplified. No more connection
to the database at that point. Fees are determined based on incoming and
outgoing amounts.

routing/heap.go

@@ -78,9 +78,9 @@ type path struct {
 	// that the path requires.
 	dist int
 
-	// hops is an ordered list of edge that comprises a potential payment
+	// hops is an ordered list of edges that comprises a potential payment
 	// path.
-	hops []*ChannelHop
+	hops []*channeldb.ChannelEdgePolicy
 }
 
 // pathHeap is a min-heap that stores potential paths to be considered within