Remove stbt.Keyboard.Selection type
Remove stbt.Keyboard.Selection type

The user's Page Object's `selection` property should return a `Key` type
directly, by calling `Keyboard.find_key()`.

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester