Merge changes from topic "vpn_data_accnt_revert"

* changes:
  Revert "Take all VPN underlying networks into account when migrating traffic for"
  Revert "NetworkStatsService: Fix getDetailedUidStats to take VPNs into account."
  Revert "Addressing comments for http://ag/7700679."
  Revert "Add one more test for VPN usage stats."