healthd: Remove access to /sys/class/power_supply/battery/batt_vol and batt_temp

These are custom paths from early Android devices that the framework used to
read, and that code was copied into healthd. Removed because this is not
defined in upstream kernel.

Change-Id: I375a8a62610c1235d82c1f27568437b16e0f96a8
Fixes: 72824944
Test: health 2.0 VTS test