Revert "Backup/restore recents task list"

Reverts commits 92dd1abe,
18795a22, and
ac6a3a5e which make-up
changes required for backing-up and restoring recent
tasks from one device to another.

The implementation had too many unresolved issues including
the ordering of the restored recent tasks which was depending
on when the task package is installed on the new device that
puts the restored recents list out of order compared to the
old device.

Bug: 15986349
Bug: 19014377
Bug: 20763296

Change-Id: I06fd35a43036ef0b7260cf4db9c42890df63b95d