RFR: 8344086: Remove security manager dependency in FFM

[Per Minborg]

This PR proposes to remove the security manager dependencies in the FFM implementing classes.

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Commit messages:
 - Remove security manager related code

Changes: https://git.openjdk.org/jdk/pull/22071/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22071&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344086
  Stats: 72 lines in 11 files changed: 5 ins; 33 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/22071.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22071/head:pull/22071

PR: https://git.openjdk.org/jdk/pull/22071