routing: move ErrMaxRouteHopsExceeded check

Now that SendToRoute is no longer using the payment lifecycle, we move
the max hop check out of the payment shard's launch() method, and return
the error directly, such that it can be handled in SendToRoute.

routing/payment_lifecycle.go

@@ -139,24 +139,6 @@ func (p *paymentLifecycle) resumePayment() ([32]byte, *route.Route, error) {
 			// With the route in hand, launch a new shard.
 			var outcome *launchOutcome
 			attempt, outcome, err = shardHandler.launchShard(rt)
-
-			// With SendToRoute, it can happen that the route exceeds protocol
-			// constraints. Mark the payment as failed with an internal error.
-			if err == route.ErrMaxRouteHopsExceeded ||
-				err == sphinx.ErrMaxRoutingInfoSizeExceeded {
-
-				log.Debugf("Invalid route provided for payment %x: %v",
-					p.paymentHash, err)
-
-				controlErr := p.router.cfg.Control.Fail(
-					p.paymentHash, channeldb.FailureReasonError,
-				)
-				if controlErr != nil {
-					return [32]byte{}, nil, controlErr
-				}
-			}
-
-			// In any case, don't continue if there is an error.
 			if err != nil {
 				return [32]byte{}, nil, err
 			}