RFR: 8355522: Remove the `java.locale.useOldISOCodes` system property [v6]

[Naoto Sato]

> This PR removes the system property deprecated in JDK 25. If the property is specified at runtime, a warning will be emitted at startup to inform the user that the value is ignored. A corresponding CSR has been drafted as well

Naoto Sato has updated the pull request incrementally with one additional commit since the last revision:

  Apply suggestions from code review
  
  Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26419/files
  - new: https://git.openjdk.org/jdk/pull/26419/files/965830aa..c427e188

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26419&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26419&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26419.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26419/head:pull/26419

PR: https://git.openjdk.org/jdk/pull/26419