Remove references to options.environment in tutorials

[SimonWoolf]

The root of the confusion in https://support.ably.io/a/tickets/105174 is that the push notifications tutorials https://www.ably.io/tutorials/android-push-direct-registration#step4 and https://docs.ably.io/tutorials/android-push-server-registration/ still have references to options.environment = BuildConfig.ABLY_ENV, presumably because we'd told the tutorial author to use the sandbox env. They just shouldn't be there in the final tutorial, they only serve to confuse people. 99% of people don't need to know we even have other clusters