Convert DirectorySelection sample to AndroidX

Test cases were using ActivityInstrumentationTestCase2 which was
deprecated (in API 24) and (seemingly) removed. Since the test cases
will need to be rewritten anyway, I've removed them for the time being.

Bug: 117822353
Test: Manually verified

Change-Id: I40a62a3287d11bc5c7658f5395148d510cfda738