Fix incorrect GMT offset in display

- android.icu.impl.TimeZoneAdapter doesn't fully implement
java.util.TimeZone, e.g. does not override getOffset(long date).
TimeZoneAdapter isn't a public API in ICU/Android. It shouldn't be
used in the first place

Bug: 77223510
Test: m RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.datetime.timezone
Change-Id: Ic0d7794326948796dcc5cc0b268ef634a74803c4