Correct sample for delete subnet

Author: haphan

samples/networking/v2/subnets/delete.php

@@ -18,6 +18,6 @@
 
 $networking = $openstack->networkingV2();
 
-$network = $networking->getSubnet('{subnetId}');
+$subnet = $networking->getSubnet('{subnetId}');
 
-$network->delete();
+$subnet->delete();