RFR: JDK-8264655: Minor internal doc comment cleanup

[Jonathan Gibbons]

Please review some minor updates to internal doc comments on javadoc code. 

In addition, since this is just a cleanup PR, some redundant modifiers noted by an IDE have been removed.

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Commit messages:
 - JDK-8264655: Minor internal doc comment cleanup

Changes: https://git.openjdk.java.net/jdk/pull/3327/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3327&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264655
  Stats: 18 lines in 4 files changed: 1 ins; 3 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3327.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3327/head:pull/3327

PR: https://git.openjdk.java.net/jdk/pull/3327