RFR: 8345048: Remove the jmx.extend.open.types compatibility property

[Kevin Walls]

Classes should not override javax.management.openmbean.OpenType.getClassName(), and this was made illegal (caused an Exception) in JDK6.  A System Property jmx.extend.open.types was introduced to allow such an override, for compatibility reasons.

This was not documented but was mentioned in the Exception message.

This compatibility convenience flag should be removed.

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Commit messages:
 - 8345048: Remove the jmx.extend.open.types compatibility property

Changes: https://git.openjdk.org/jdk/pull/23151/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23151&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345048
  Stats: 5 lines in 1 file changed: 0 ins; 3 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23151.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23151/head:pull/23151

PR: https://git.openjdk.org/jdk/pull/23151