RFR: 8299978: Remove MethodHandleNatives.getMembers

[Claes Redestad]

This removes `MethodHandleNatives.getMembers`, which has fallen into disuse.

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Commit messages:
 - 8299978: Remove MethodHandleNatives.getMembers

Changes: https://git.openjdk.org/jdk/pull/11949/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11949&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299978
  Stats: 172 lines in 4 files changed: 0 ins; 171 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11949.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11949/head:pull/11949

PR: https://git.openjdk.org/jdk/pull/11949