RFR: 8336152: Remove unused forward declaration in classLoadInfo.hpp

[Zhengyu Gu]

A trivial cleanup

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Commit messages:
 - 8336152: Remove unused forward declaration in classLoadInfo.hpp

Changes: https://git.openjdk.org/jdk/pull/20130/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20130&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336152
  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20130.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20130/head:pull/20130

PR: https://git.openjdk.org/jdk/pull/20130