Use a-c Robolectric ADM shadows

[dnarcese]

⛔️ Blocked on https://github.com/mozilla-mobile/android-components/issues/4188.

Vision statement / What / Requirements

We implemented 3 ADM shadow classes for Robolectric unit tests (find them in this folder). Once they move to a-c, we can remove them here and use a-c's.

Impact

Extra classes that are unnecessary.

Acceptance criteria

Our 3 ADM shadow classes are removed and instead we use a-c's.