Not call MainSwitchBar.getSwitch()

This is private implement details, will be removed in future.

Should call MainSwitchBar's isChecked() and setChecked() to ensure
main switch bar's style is set correctly.

Bug: 306658427
Test: manual - on wifi tether
Test: manual - on developer options
Test: m RunSettingsRoboTests
Change-Id: I292ffbcf73da0721fc206e3dac7610a0aeb20047