Align Simple Offline Map Example with Expectations

[riastrad]

Currently the simple offline example is set to delete the region when the app is backgrounded or closed. Although this was most likely implemented so as to not pollute the database,and make it possible to start the download again without clearing the app's database (which makes manual testing easier), the behavior is counterintuitive for users who are trying to understand how offline functionality should behave.

Rather than have this be the default behavior and possible cause unnecessary developer confusion, we should have a button in the test activity that clears the offline data when tapped.

cc: @mapbox/maps-android

[langsmith]

Thanks @riastrad