Mute BatteryStatsImpl CPU uid readers log

As requested in b/170786671
These two print statements are happening 10s of times every 5s.

10-13 19:21:45.964 W BatteryStatsImpl: Got cluster times for an isolated
uid with no mapping: 1099185
10-13 19:21:51.445 D BatteryStatsImpl: Got freq readings for an isolated
uid with no mapping: 90001

Bug: 165017936
Test: n/a
Change-Id: Ib1e7bc097e4864ce16f3622b780675609776cb30