Use OneHandedSettingsUtil static utils directly

Removes dagger injection pattern of OneHandedSettingsUtil since it's
util class that provide static function.

Removes testRegisterSettingsObserver_forXXX tests in OneHandedUITest
given that the logic should be covered by tesSettingsObserver_updateXXX.

Fix: 163015578
Test: atest OneHandedUITest
Test: atest OneHandedSettingsUtilTest
Change-Id: I34524bfcddf6d7411d23532c4ff027c4d9e62197