itest: remove unnecessary channel close and node shutdown

Since we don't have standby nodes anymore, we don't need to close the
channels when the test finishes. Previously we would do so to make sure
the standby nodes have a clean state for the next test case, which is no
longer relevant.

itest/lnd_hold_persistence_test.go

@@ -35,7 +35,7 @@ func testHoldInvoicePersistence(ht *lntest.HarnessTest) {
 
 	// Open a channel between Alice and Carol which is private so that we
 	// cover the addition of hop hints for hold invoices.
-	chanPointAlice := ht.OpenChannel(
+	ht.OpenChannel(
 		alice, carol, lntest.OpenChannelParams{
 			Amt:     chanAmt,
 			Private: true,
@@ -222,8 +222,4 @@ func testHoldInvoicePersistence(ht *lntest.HarnessTest) {
 				"wrong failure reason")
 		}
 	}
-
-	// Finally, close all channels.
-	ht.CloseChannel(alice, chanPointBob)
-	ht.CloseChannel(alice, chanPointAlice)
 }