RFR: 8345213: JVM Prefers /etc/timezone Over /etc/localtime on Debian 12

[Naoto Sato]

Removing the support for /etc/timezone file that is Debian distro specific. The file is no longer considered authoritative (https://wiki.debian.org/TimeZoneChanges#Check_Configured_Timezone), and in fact, it is now out of sync as the bug reports. The fix was confirmed manually on a Ubuntu 25.04.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/23755/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23755&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345213
  Stats: 30 lines in 1 file changed: 0 ins; 28 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23755.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23755/head:pull/23755

PR: https://git.openjdk.org/jdk/pull/23755