RFR: 8304989: unnecessary dash in @param gives double-dash in docs

[Jaikiran Pai]

Can I please get a review of this trivial doc-only change that addresses https://bugs.openjdk.org/browse/JDK-8304989?

I ran `make docs-image` with this change and the generated javadocs look fine.

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Commit messages:
 - 8304989: unnecessary dash in @param gives double-dash in docs

Changes: https://git.openjdk.org/jdk/pull/13204/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13204&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304989
  Stats: 8 lines in 3 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/13204.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13204/head:pull/13204

PR: https://git.openjdk.org/jdk/pull/13204