Settings: Use correct LOW_POWER_MODE_TRIGGER default

* Low power mode was set to never enable automatically upstream in
  frameworks/base. We erroneously read from the
  config_lowBatteryWarningLevel resource for the default in change:
  821fd62d, which is usually 15.
* Reset this to 0 to align with the default value set in the provider.

REF: CYNGNOS-2274
Change-Id: Iec32f972fe6d67b258ee17eff603c4a67c99d783