Previously getISOFields() was used to get the exact value of the
[[Calendar]] and [[TimeZone]] internal slots, as well as to get the
reference ISO year for PlainMonthDay and reference ISO day for
PlainYearMonth.
Use calendarId and timeZoneId for the former and toString() for the
latter.
Many tests tested some functionality while asserting that there were no
calls of calendar or time zone methods. We can continue testing the
functionality, but there are no more methods to call, so we can delete
those parts of the tests.
Temporarily replace them with getISOFields().calendar/timeZone just to
keep the tests running until we remove Calendar and TimeZone objects
altogether.
See: tc39/proposal-temporal#2826
