Remove some usages of `GroupTask.task2`

This CL marks `GroupTask.task1` and `GroupTask.task2` as deprecated, and
removes some of the usages of the `task2`. Follow-up CLs will continue
replacing all the usages.

Bug: 388593902
Test: m
Flag: EXEMPT pure refactor with no behavior change.
Change-Id: I530bbba00bd41cf33a952b083de7670d9a490e81