Revert "Make sure all runtime threads are in the System thread group."

This reverts commit 0e01c8d3f3c2d7cc4ac2cf5cf01ae913a4c6181e.

Bug: 146178357
Reason for revert: Breaks on debug-gc

Change-Id: I2a305a271ef50263c2a722114f686a478d931c22
11 files changed