RFR: 8267465: remove superfluous preview related annotations and test options

[Vicente Romero]

Please review this PR which is removing several superfluous `@SuppressWarnings("preview")` annotations from the compiler code and also removing preview related, but not needed anymore, options from regression tests. Please also review the related CSR which covers the only case that modified a public API.

TIA

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Commit messages:
 - 8267465: remove superfluous @SuppressWarnings(preview) annotations

Changes: https://git.openjdk.java.net/jdk/pull/4330/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4330&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267465
  Stats: 111 lines in 33 files changed: 0 ins; 86 del; 25 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4330.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4330/head:pull/4330

PR: https://git.openjdk.java.net/jdk/pull/4330