Delete unnamed sound (#7214)

# About the pull request

Removes a sound without a name (`sound/effects/.wav`) that is never
used.

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# Explain why it's good for the game

Even in the PR that introduced it
(#6492) never used it, and it
has no description or purpose.
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
No player facing changes.