Remove CallLogActivity.

CallLogActivity was only used by tests. Instead, extend
FragmentTestActivity to handle loading of an arbitrary fragment into it,
so that we can test the CallLogFragment within it.

So far, FragmentTestActivity was only used with a UI-less fragment,
which therefore did not need a placeholder for the fragment.

Bug: 5286366
Change-Id: I939d6fb212621345b8a1ba4ec1a3b1c56909ce50