Fix review comments location_time_zone_detection

Fix review comments for location_time_zone_detection.xml and associated
classes from http://ag/12792958.

Bug: 152746236
Test: Manual: build / boot / toggle switch in SettingsUI / inspect output of adb shell dumpsys time_zone_detector
Test: Manual: build / boot / install TestDPC / toggle switch in work profile in SettingsUI / inspect output of adb shell dumpsys time_zone_detector
Test: m -j30 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.location.TimeZoneDetectionPreferenceControllerTest"
Test: m -j30 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.location.LocationTimeZoneDetectionPreferenceControllerTest"
Test: m -j30 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.location.TimeZoneDetectionSettingsTest"
Change-Id: I641f312cd63359f45664a93e009e5a975dbd6485