multi: ensure that BlockEpoch clients are cancelled

This commit fixes a prior goroutine leak that could result in a node
having thousands of goroutines, particularly due to many concurrent
channel fundings. We now ensure that for each BlockEpoch client
created, we ensure that the client is cancelled once the creating
grouting exits.

fundingmanager.go

@@ -1210,6 +1210,8 @@ func (f *fundingManager) waitForFundingWithTimeout(completeChan *channeldb.OpenC
 		return
 	}
 
+	defer epochClient.Cancel()
+
 	waitingDoneChan := make(chan struct{})
 	cancelChan := make(chan struct{})
 

utxonursery.go

@@ -321,6 +321,7 @@ func (u *utxoNursery) incubator(newBlockChan *chainntnfs.BlockEpochEvent,
 	startingHeight uint32) {
 
 	defer u.wg.Done()
+	defer newBlockChan.Cancel()
 
 	currentHeight := startingHeight
 out: