RFR: 8345984: Remove redundant checkXXX methods from java.management Util class

[Kevin Walls]

A post-SecurityManager removal cleanup task, to remove checkAccess(), checkMonitorAccess() and checkControlAccess() from src/java.management/share/classes/sun/management/Util.java (methods are already no-ops).

While here, there are a few imports of Util that are unnecessary.

No changes to the module visibility/exports.

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Commit messages:
 - unused imports
 - 8345984: Remove redundant checkXXX methods from java.management Util class

Changes: https://git.openjdk.org/jdk/pull/22680/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22680&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345984
  Stats: 15 lines in 4 files changed: 0 ins; 15 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22680.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22680/head:pull/22680

PR: https://git.openjdk.org/jdk/pull/22680