After ag/2573096, the batterystats will be refreshed after each
broadcastReceiver registeration. And this registeration happens
in onResume().
So we don't need to init batterystats in onCreate() anymore.
Bug: 65629008
Test: RunSettingsRoboTests
Change-Id: I4ed2d420c6f2bb77d726dac4dd58fa6704ce6929