utxonursery: remove unused commit sweep code

Now that the commit sweep resolver is no longer relying on the nursery,
all code associated with commit sweeping can be removed.

server.go

@@ -847,7 +847,6 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 			return nil
 		},
 		IncubateOutputs: func(chanPoint wire.OutPoint,
-			commitRes *lnwallet.CommitOutputResolution,
 			outHtlcRes *lnwallet.OutgoingHtlcResolution,
 			inHtlcRes *lnwallet.IncomingHtlcResolution,
 			broadcastHeight uint32) error {
@@ -864,7 +863,7 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 			}
 
 			return s.utxoNursery.IncubateOutputs(
-				chanPoint, commitRes, outRes, inRes,
+				chanPoint, outRes, inRes,
 				broadcastHeight,
 			)
 		},