RFR: 8351165: Remove unused includes from vmStructs

Tue Mar 4 13:02:06 UTC 2025

Please review this trivial change to remove some unneeded includes and type declarations from vmStructs.  The SystemDictionary type is unused because classes are looked up in the ClassLoaderDataGraph in the SA, and they haven't been in a single SystemDictionary for a very long time.
Tested with SA tests locally.

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Commit messages:
 - 8351165: Remove unused includes from vmStructs

Changes: https://git.openjdk.org/jdk/pull/23897/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23897&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351165
  Stats: 17 lines in 2 files changed: 0 ins; 15 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23897.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23897/head:pull/23897

PR: https://git.openjdk.org/jdk/pull/23897