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

itest/lnd_zero_conf_test.go

@@ -865,15 +865,6 @@ func testOptionScidUpgrade(ht *lntest.HarnessTest) {
 	daveInvoice2 := dave.RPC.AddInvoice(daveParams)
 	ht.CompletePaymentRequests(bob, []string{daveInvoice2.PaymentRequest})
 
-	// TODO(yy): remove the sleep once the following bug is fixed.  When
-	// the payment is reported as settled by Bob, 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(2 * time.Second)
-
 	// Close standby node's channels.
 	ht.CloseChannel(bob, fundingPoint2)
 }