Revert "Finish activity when created by documents provider and documents provider gone."

This reverts commit c85758f9.

Reason for revert: b/172945037. Also the same effect can be achieved by setting intent flags Intent.FLAG_ACTIVITY_CLEAR_TASK (example cl/301927723) so this change is not necessary (it was precautionary from the first place).

Change-Id: I4b34af961c98ff69bdc570f88edec18df19f8171