Remove test for unsupported GregorianCalendar functionality.

Also adds an explanatory comment and makes the
intent of the implementation clearer without changing
any of the functionality.

TL;DR - there doesn't appear to be any sensible way
to provide any sort of consisent semantics if we plan
on supporting these fields.

Partial cherry-pick from commit
5eea675931db0bf976c2347f4e3b7e4703d337a4.
The implementation is left unmodified.

bug: 12778197
Change-Id: I0f161967412a42c582ba60da1c96d0ce37a90bcf
1 file changed