RFR: 8327729: Remove deprecated xxxObject methods from jdk.internal.misc.Unsafe

[Eirik Bjørsnøs]

Please review this PR which removes the 19 deprecated `xxObject*` alias methods from `jdk.internal.misc.Unsafe`.

These methods were added in JDK-8213043 (JDK 12), presumably to allow `jsr166.jar` to be used across JDK versions. This was a follow-up fix after JDK-8207146 had renamed these methods to `xxReference*'.

Since OpenJDK is now the single source of truth for `java.util.concurrent`, time has come to remove these deprecated alias methods.

Testing: This is a pure deletion of deprecated methods, so the PR includes no test changes and the `noreg-cleanup` label is added in the JBS. I have verified that all `test/jdk/java/util/concurrent/*` tests pass.

Tagging @DougLea and @Martin-Buchholz to verify that this removal is timely.

-------------

Commit messages:
 - Remove deprecated xxObject methods from jdk.internal.misc.Unsafe

Changes: https://git.openjdk.org/jdk/pull/18176/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18176&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327729
  Stats: 87 lines in 1 file changed: 0 ins; 87 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18176.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18176/head:pull/18176

PR: https://git.openjdk.org/jdk/pull/18176