core: Eliminate ISO 8601 formatting workaround for dates

Google have fixed the issue upstream, so the workaround is no longer
needed. Thanks Google!

https://bugzilla.gnome.org/show_bug.cgi?id=737799
https://code.google.com/a/google.com/p/apps-api-issues/issues/detail?id=3595
tests: Remove pointless async authorizer tests from contacts.c

The authorisers are tested separately, and don’t need to be re-tested in
each unit test suite.
tests: Update Contacts test traces for ISO 8601 date changes

https://bugzilla.gnome.org/show_bug.cgi?id=737799
tests: Temporarily disable some Contacts test assertions

Seems these elements broke on the server at some point.

https://code.google.com/a/google.com/p/apps-api-issues/issues/detail?id=3662