Avoid load icon and label in the background for periodic job

In the original design, BatteyEntry will load icon and label in the
background thread and cache them into memory, but we don't need such
information in the periodic fetching job. Add a method to disable it to
improve the performance and memory footprint.

Bug: 185207505
Test: make SettingsRoboTests
Test: make SettingsGoogleRoboTests
Change-Id: Iba759256e94159fce243ff4d700a8adf9e92f82c