[R] clean-up date time unit testing once tzdb is available on Windows

[asfimport]

We are skipping a high number of tests on Windows due to the tz database not being available. Once ARROW-13168 is solved, we need to have a thorough look at the skipped tests / reduced functionality.

Reporter: Dragoș Moldovan-Grünfeld / @dragosmg
Assignee: Dragoș Moldovan-Grünfeld / @dragosmg

Related issues:

• [C++] Timezone database configuration and access (relates to)

PRs and other links:

• GitHub Pull Request #12883

_{Note: This issue was originally created as ARROW-16073. Please see the migration documentation for further details.}

[asfimport]

Jonathan Keane / @jonkeane:
If we haven't done this already, we should definitely do it before the release to catch if we've introduced any regressions with our liberal use of skip on windows...

[asfimport]

Krisztian Szucs / @kszucs:
Postponing to 9.0

[asfimport]

Jonathan Keane / @jonkeane:
Issue resolved by pull request 12883
#12883