RFR: 8283092: JMX subclass permission check redundant with strong encapsulation

[Kevin Walls]

Removing permission checks which, in the presence of a Security Manager, would check for a RuntimePermission "className.subclass".  This was to prevent subclassing these classes, but is no longer necessary with strong encapsulation from modules.

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Commit messages:
 - 8283092: JMX subclass permission check redundant with strong encapsulation

Changes: https://git.openjdk.java.net/jdk/pull/7827/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7827&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283092
  Stats: 31 lines in 3 files changed: 0 ins; 28 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7827.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7827/head:pull/7827

PR: https://git.openjdk.java.net/jdk/pull/7827