Remove call to Dependency.get() from BatteryControllerImpl.

This specifically targets Dependendy.get(BG_HANDLER) and
Dependendy.get(MAIN_HANDLER), though some other related refactoring
is undertaken along the way.

Bug: 141882822
Test: atest SystemUITests
Change-Id: I93b70534c262bff87333c0491e0def2ca2db8ac8
3 files changed