Revert "Use Service handler thread for NetworkStatsObservers"

This reverts commit 8b1d824ad2e3dd3e14b87f2883d36f0b6a6bc213.

Reason for revert: b/332214348


Fix: 332214348
Change-Id: Iac8b9a11fb5b1c2e704eada62869c8c8552b3804
4 files changed