Follow class package change: LocaleList

In order to avoid layering violation, LocaleList needs to be moved from
android.util package to android.os package [1].  This CL follows up that
package change.

No behavior change is intended.

 [1]: Ia8de2ee9df3dd0a42b1fe84574439519b680fe18

Bug: 28819696
Change-Id: Ie795c191e299358c7c463693823f309ce61cc985