RFR: 8248318: Examine the use of boxing in ObjectStreamClass

[Julia Boes]

This change removes some instances of superfluous boxing in java.io.ObjectStreamClass.
Testing: tier 1-3 all clear.

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Commit messages:
 - remove superfluous boxing

Changes: https://git.openjdk.java.net/jdk/pull/2641/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2641&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248318
  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2641.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2641/head:pull/2641

PR: https://git.openjdk.java.net/jdk/pull/2641