sweep: remove redundant notifications during shutdown

This commit removes the hack introduced in lightningnetwork#4851. Previously we had this
issue because the chain notifier was stopped before the sweeper, which
was changed a while back and we now always stop the chain notifier last.
In addition, since we no longer subscribe to the block epoch chan
directly, this issue can no longer happen.

sweep/sweeper.go

@@ -454,38 +454,7 @@ func (s *UtxoSweeper) Start() error {
 
 	// Start sweeper main loop.
 	s.wg.Add(1)
-	go func() {
-		defer s.wg.Done()
-
-		s.collector()
-
-		// The collector exited and won't longer handle incoming
-		// requests. This can happen on shutdown, when the block
-		// notifier shuts down before the sweeper and its clients. In
-		// order to not deadlock the clients waiting for their requests
-		// being handled, we handle them here and immediately return an
-		// error. When the sweeper finally is shut down we can exit as
-		// the clients will be notified.
-		for {
-			select {
-			case inp := <-s.newInputs:
-				inp.resultChan <- Result{
-					Err: ErrSweeperShuttingDown,
-				}
-
-			case req := <-s.pendingSweepsReqs:
-				req.errChan <- ErrSweeperShuttingDown
-
-			case req := <-s.updateReqs:
-				req.responseChan <- &updateResp{
-					err: ErrSweeperShuttingDown,
-				}
-
-			case <-s.quit:
-				return
-			}
-		}
-	}()
+	go s.collector()
 
 	return nil
 }