itest: update wipe_forwarding_packages test for deferred cleanup

Update the testWipeForwardingPackages integration test to restart the
nodes after channel closure confirmation. This is necessary because
forwarding packages are now deleted during CleanupPendingCloses at
startup, rather than during CloseChannel.

Author: ziggie1984

itest/lnd_wipe_fwdpkgs_test.go

@@ -81,6 +81,11 @@ func testWipeForwardingPackages(ht *lntest.HarnessTest) {
 	// Mine 1 block to get the two closing transactions confirmed.
 	ht.MineBlocksAndAssertNumTxes(1, 2)
 
+	// Restart the nodes to trigger CleanupPendingCloses, which deletes
+	// the forwarding packages for closed channels.
+	ht.RestartNode(bob)
+	ht.RestartNode(alice)
+
 	// Now that the closing transaction is confirmed, the above waiting
 	// close channel should now become pending force closed channel.
 	pendingAB = ht.AssertChannelPendingForceClose(bob, chanPointAB).Channel