RFR: 8304990: unnecessary dash in @param gives double-dash in docs

[Lance Andersen]

Please review this trivial change which removes a redundant `-` from an `@param` and cleans up the formatting  for the `invalid` method.


It looks like there is some additional formatting clean up that can be done but I will handle that under a separate PR.

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Commit messages:
 - Remove extra -

Changes: https://git.openjdk.org/jdk/pull/13217/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13217&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304990
  Stats: 6 lines in 1 file changed: 0 ins; 1 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/13217.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13217/head:pull/13217

PR: https://git.openjdk.org/jdk/pull/13217