RFR: 8332303: Better JMX interoperability with older JDKs, after removing Subject Delegation

[Kevin Walls]

Running JConsole from a previous JDK, and attaching to jdk-23 (after [JDK-8326666](https://bugs.openjdk.org/browse/JDK-8326666): Remove the Java Management Extension (JMX) Subject Delegation feature), the MBean tab is blank.

In javax/management/remote/rmi/RMIConnectionImpl.java:
addNotificationListener rejects a non-null delegationSubjects array, but older JDKs will send such an array. It could accept the array, and only reject/throw if it contains a non-null Subject (i.e. if an attempt to use subject delegation is really happening).

Manually testing JConsole, the MBean tab is fully populated and usable.

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Commit messages:
 - Remove unnecessary Subject array in RMIConnectionImpl, update docs in RMIConnection
 - JConsole's MBean tab is blank after JMX Subject Delegation removal.

Changes: https://git.openjdk.org/jdk/pull/19253/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19253&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332303
  Stats: 18 lines in 2 files changed: 9 ins; 2 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/19253.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19253/head:pull/19253

PR: https://git.openjdk.org/jdk/pull/19253