RFR: 8344228: Revisit SecurityManager usage in java.net.http after JEP 486 integration

[Daniel Fuchs]

Please find here a patch that cleans up the java.net.http module code to remove permission checks and doPriviliged calls.
This was mostly mechanical.

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Commit messages:
 - 8344228: Revisit SecurityManager usage in java.net.http after JEP 486 integration

Changes: https://git.openjdk.org/jdk/pull/22118/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22118&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344228
  Stats: 732 lines in 25 files changed: 3 ins; 650 del; 79 mod
  Patch: https://git.openjdk.org/jdk/pull/22118.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22118/head:pull/22118

PR: https://git.openjdk.org/jdk/pull/22118