RFR: 8304988: unnecessary dash in @param gives double-dash in docs

[Jaikiran Pai]

Can I please get a review of this trivial doc only change which addresses https://bugs.openjdk.org/browse/JDK-8304988?

I've run `make docs-image` after this change and the generated javadoc for this class looks fine.

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Commit messages:
 - 8304988: unnecessary dash in @param gives double-dash in docs

Changes: https://git.openjdk.org/jdk/pull/13239/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13239&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304988
  Stats: 9 lines in 1 file changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/13239.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13239/head:pull/13239

PR: https://git.openjdk.org/jdk/pull/13239