RFR: 8321729: Remove 'orb' field in RMIConnector

[Kevin Walls]

Tidyup change, looks like this field was not removed when IIOP was removed from RMIConnector.

The field is not required for interoperability: 
with the field removed, I can still connect an older JMX client to a running app with the updated JDK.

Since the JDK9 change https://hg.openjdk.org/jdk9/jdk9/jdk/rev/09daaf1e4c53
did not change serialVersionUID, this update does not either.

Tests continue to pass, e.g.
javax/management (including remote which has RMI tests)
jdk/com/sun/management

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Commit messages:
 - 8321729: Remove orb field in RMIConnector

Changes: https://git.openjdk.org/jdk/pull/17055/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17055&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321729
  Stats: 6 lines in 1 file changed: 0 ins; 6 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17055.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17055/head:pull/17055

PR: https://git.openjdk.org/jdk/pull/17055