Update tzdata to version 2021a

[Brian Murray]

New upstream version affecting the following timestamp:
$region/$timezone = Africa/Juba
Verification is done with 'zdump'. The first timezone that gets changed in the updated package is dumped with 'zdump -v $region/$timezone_that_changed' (this needs to be greped for in /usr/share/zoneinfo/). [For example: 'zdump -v Africa/Juba'.] This is compared to the same output after the updated package got installed. If those are different the verification is considered done.
[Test Case for all releases]
1) zdump -v Africa/Juba | grep 2021
For releases with ICU timezone data verification is done using the following with dates before and after the change:[Test Case for releases >= 20.04 LTS]
1) sudo apt-get install python3-icu
2) python3 -c 'from datetime import datetime; from icu import ICUtzinfo, TimeZone; tz = ICUtzinfo(TimeZone.creat eTimeZone('Africa/Juba')); print(str(tz.utcoffset(datetime(2021, 2, 1))))'
Additionally, an upstream update of tzdata removed the 'old' SystemV timezones, so we should ensure that they are kept in Ubuntu 20.04 LTS and earlier releases. Subsequently, these should be checked for using the following:
[Test Case for releases <= 20.04 LTS]
diff <(zdump -v America/Phoenix | cut -d' ' -f2-) <(zdump -v SystemV/MST7 | cut -d' ' -f2-)
Nothing should be returned by the above command.