Add 'deleted' state in _subscription_users.py

[TheTechAlchemist]

Hello,

as documented in https://developer.paddle.com/api-reference/subscription-api/users/listusers and https://developer.paddle.com/reference/platform-parameters/event-statuses , there is also the "deleted" status - useful to retrieve informations about cancelled subscriptions.

At the moment is impossible to call the list_subscription_users() function with state='deleted', because it's not listed in the states list on line 25 of _subscription_users.py

Can you please add it?

Thank you