Allow un-assigning schedule from wiser.assign_schedule service

[bfayers]

I need the ability to un-assign the schedule from the service as well as assigning. I noticed it's possible over the HASS websocket by setting remove: true, but that isn't implemented in the service.

[msp1974]

Added in v3.4.7 to allow you to assign an id of 0 to room/device to remove assigned schedule. See wiki notes for usage.

https://github.com/asantaga/wiserHomeAssistantPlatform/wiki/Services#assign-schedule