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

This reverts commit 1414a0d4d8b5254755184333d38118f1a2c16873.

Reason for revert: reversions of CLs from http://b/174776875 removed dependencies for this CL, and made the freezer non-functional. This CL has to be reverted as well

Bug:174776875
Change-Id: Idbd9532374bb661330b3c7546bbdf086a046aba3
2 files changed