Track tzdb 2020a changes [N MR1 CTS branch]

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.

Bug: 157444326
Test: See the associated system/timezone change
Merged-In: Icdbab139b91b5882b42d986b6b85bd9cef41dcf0
Change-Id: Icdbab139b91b5882b42d986b6b85bd9cef41dcf0
(cherry picked from commit 4460d9770f8677318966548a987fe20ebbefd3cf)
(cherry picked from commit 3a721979e3bf17ba4854270b7edc740536e50aa1)
(cherry picked from commit bed279e1091f60404d3ba9034a99e6a47674d77d)
(cherry picked from commit c16f4d6f2cfafad7650a15cfdb57566400bc618a)
(cherry picked from commit 9b207b42dca7e3d5a5cebad7232a087d5a6ce1eb)
1 file changed