RFR: 8348265: RMIConnectionImpl: Remove Subject.callAs on MarshalledObject

[Kevin Walls]

Redundant after Security Manager removal, remove the Subject.callAs() call on a MashalledObject.cast().
Previously, a Policy could possibly have restricted permissable classes available to the cast().

Nothing in our tests fails if we remove the callAs.

Also fixing a comment typo ("reqIncomming") and rewording that comment.

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Commit messages:
 - 8348265: RMIConnectionImpl: Remove Subject.callAs on MarshalledObject

Changes: https://git.openjdk.org/jdk/pull/23230/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23230&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348265
  Stats: 15 lines in 1 file changed: 0 ins; 13 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23230.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23230/head:pull/23230

PR: https://git.openjdk.org/jdk/pull/23230