RFR: 8255862: Remove @SuppressWarnings from sun.misc.Unsafe

[Mandy Chung]

Record classes are now a standard feature in 16. @SuppressWarnings can be
removed from sun.misc.Unsafe.

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Commit messages:
 - 8255862: Remove @SuppressWarnings from sun.misc.Unsafe

Changes: https://git.openjdk.java.net/jdk/pull/1049/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1049&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255862
  Stats: 6 lines in 1 file changed: 0 ins; 3 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1049.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1049/head:pull/1049

PR: https://git.openjdk.java.net/jdk/pull/1049