Revert^3 "libprocessgroup: move freezer to uid/pid hierarchy"

This reverts commit 7707909ba26805d1c8453c2856a983a38ce26097.
Bug: 179006802
Test: verified correct functioning of the freezer after reverting

Change-Id: I848146a18a0879010abf5b00e7081f2771059064
2 files changed