Delete ChoicePromptHandlerTests and InputPromptHandlerTests (#1660)

These tests would need to be rewritten for the new APIs, that is, they
cannot simply be massaged and turned back on as the interfaces they were
exercising have changed. Fortunately `$host.UI.PromptForChoice(...)`
works as expected, but is not high priority to cover in new tests.

Author: andyleejordan