Use libprocessgroup to find cgroup v2 paths

Cgroup v2 paths are owned by libprocessgroup. Those paths can change
based on build flags, so paths generated outside of libprocessgroup may
not always be correct.

Additionally, the cpuacct controller has not been mounted at /acct since
2018 with commit 192aee782 ("libprocessgroup: Add support for task
profiles"), so remove the broken "v1" support.

Bug: 382693152
Flag: EXEMPT refactor
Test: atest FrameworksMockingServicesTests:AppChildProcessTest
Test: atest CtsAppTestCases:ActivityManagerTest
Change-Id: Ibd187b2d784ef4cb40099f30cd95206fb0536a98
Merged-In: Ibd187b2d784ef4cb40099f30cd95206fb0536a98