<i18n dev> RFR: 8313813: Field sun.util.calendar.CalendarDate#forceStandardTime is never set

Wed Sep 13 18:00:04 UTC 2023

Please review this PR which is a continuation of [JDK-6453901](https://bugs.openjdk.org/browse/JDK-6453901) to remove unused code from the _sun.util.Calendar_ classes.

`forceStandardTime` is always false.

In addition, `locale` is never by used by _CalendarDate_ or any inheritors and can be removed.

As a result, _ImmutableGregorianDate_ no longer needs to override the _setLocale_ method and throw UnsupportedOperationException.

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/15726/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15726&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313813
  Stats: 14 lines in 2 files changed: 0 ins; 13 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15726.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15726/head:pull/15726

PR: https://git.openjdk.org/jdk/pull/15726