RFR: 8313813: Field sun.util.calendar.CalendarDate#forceStandardTime is never set [v4]

[Justin Lu]

> 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.

Justin Lu has updated the pull request incrementally with one additional commit since the last revision:

  Clarify implementation after removal of if else block

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15726/files
  - new: https://git.openjdk.org/jdk/pull/15726/files/5a3375ec..2a2b0e7f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15726&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15726&range=02-03

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 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