RFR: 8377797: SA MethodData is unused

[Coleen Phillimore]

This change removes MethodData code copied into SA that's out of date for the valhalla repo.

Tested with tier1-3.

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Commit messages:
 - Remove vmStructs defs
 - 8377797: SA MethodData is unused

Changes: https://git.openjdk.org/jdk/pull/29693/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29693&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377797
  Stats: 2799 lines in 31 files changed: 2 ins; 2788 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/29693.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29693/head:pull/29693

PR: https://git.openjdk.org/jdk/pull/29693