Track tzdb 2020a changes [P CTS]

This commit changes a test that hardcodes knowledge of the zones with a
raw offset of UTC-8. In 2020a America/Whitehorse and America/Dawson (and
their aliases) no longer qualify.

P CTS branch notes: This change is intended to safe for devices with tzdb
2020a or earlier: it removes references to zones that have changed.

Bug: 155052221
Test: run cts-dev -m CtsLibcoreTestCases
Merged-In: Icdbab139b91b5882b42d986b6b85bd9cef41dcf0
Change-Id: Icdbab139b91b5882b42d986b6b85bd9cef41dcf0
(cherry picked from commit 40bc89f47fbf9237f2921d54ab1ef861ef4c5f32)
1 file changed