RFR: 8371885: Mark UseCompressedClassPointers as obsolete for JDK 27

[Thomas Stuefe]

Trivial patch to move the obsoletion of `UseCompressedClassPointers` to jdk 27.

Tested locally by adjusting SPECIAL_FLAG_VALIDATION_BUILD and running the `special_flags` gtest.

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Commit messages:
 - Start

Changes: https://git.openjdk.org/jdk/pull/28322/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28322&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371885
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28322.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28322/head:pull/28322

PR: https://git.openjdk.org/jdk/pull/28322