routing: move second chance logic into mission control

If nodes return a channel policy related failure, they may get a second
chance. Our graph may not be up to date. Previously this logic was
contained in the payment session.

This commit moves that into global mission control and thereby removes
the last mission control state that was kept on the payment level.

Because mission control is not aware of the relation between payment
attempts and payments, the second chance logic is no longer based
tracking second chances given per payment.

Instead a time based approach is used. If a node reports a policy
failure that prevents forwarding to its peer, it will get a second
chance. But it will get it only if the previous second chance was
long enough ago.

Also those second chances are no longer dependent on whether an
associated channel update is valid. It will get the second chance
regardless, to prevent creating a dependency between mission control and
the graph. This would interfer with (future) replay of history, because
the graph may not be the same anymore at that point.

routing/payment_session.go

@@ -52,12 +52,6 @@ type paymentSession struct {
 
 	bandwidthHints map[uint64]lnwire.MilliSatoshi
 
-	// errFailedFeeChans is a map of the short channel IDs that were the
-	// source of policy related routing failures during this payment attempt.
-	// We'll use this map to prune out channels when the first error may not
-	// require pruning, but any subsequent ones do.
-	errFailedPolicyChans map[nodeChannel]struct{}
-
 	sessionSource *SessionSource
 
 	preBuiltRoute      *route.Route
@@ -109,25 +103,7 @@ func (p *paymentSession) ReportEdgeFailure(failedEdge edge,
 //
 // TODO(joostjager): Move this logic into global mission control.
 func (p *paymentSession) ReportEdgePolicyFailure(failedEdge edge) {
-	key := nodeChannel{
-		node:    failedEdge.from,
-		channel: failedEdge.channel,
-	}
-
-	// Check to see if we've already reported a policy related failure for
-	// this channel. If so, then we'll prune out the vertex.
-	_, ok := p.errFailedPolicyChans[key]
-	if ok {
-		// TODO(joostjager): is this aggressive pruning still necessary?
-		// Just pruning edges may also work unless there is a huge
-		// number of failing channels from that node?
-		p.ReportVertexFailure(key.node)
-
-		return
-	}
-
-	// Finally, we'll record a policy failure from this node and move on.
-	p.errFailedPolicyChans[key] = struct{}{}
+	p.sessionSource.MissionControl.ReportEdgePolicyFailure(failedEdge)
 }
 
 // RequestRoute returns a route which is likely to be capable for successfully