itest+lntest: remove temporary hacks around broken coop close in itests

itest/lnd_mpp_test.go

@@ -309,15 +309,6 @@ func (m *mppTestScenario) closeChannels() {
 		return
 	}
 
-	// TODO(yy): remove the sleep once the following bug is fixed. When the
-	// payment is reported as settled by Alice, it's expected the
-	// commitment dance is finished and all subsequent states have been
-	// updated. Yet we'd receive the error `cannot co-op close channel with
-	// active htlcs` or `link failed to shutdown` if we close the channel.
-	// We need to investigate the order of settling the payments and
-	// updating commitments to understand and fix .
-	time.Sleep(5 * time.Second)
-
 	// Close all channels without mining the closing transactions.
 	m.ht.CloseChannelAssertPending(m.alice, m.channelPoints[0], false)
 	m.ht.CloseChannelAssertPending(m.alice, m.channelPoints[1], false)