RFR: 8336934: Clean up JavaLangReflectAccess

[Chen Liang]

Removed redundant APIs in `JavaLangReflectAccess` and added general warning against using `SharedSecrets`.

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Commit messages:
 - 8336934: Clean up JavaLangReflectAccess

Changes: https://git.openjdk.org/jdk/pull/20290/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20290&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336934
  Stats: 185 lines in 6 files changed: 19 ins; 147 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/20290.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20290/head:pull/20290

PR: https://git.openjdk.org/jdk/pull/20290