Hi,
'Create a snapshot' workflow has an output parameter snapshot (of type VC:VirtualMachineSnapshot) containing the created snapshot object. And the snapshot scripting type has a method removeSnapshot_Task() which you can use to remove the snapshot, using a code like:
snapshot.removeSnapshot_Task(false);
One small issue is that the output parameter snapshot cannot be accessed directly as an input in your scriptable task, but you can fix this by moving the snapshot output parameter as attribute.