docs: remove token_for from PartialUser.fetch_moderators parameters

[buck2202]

Description

just a minor documentation fixup-- token_for is documented in the parameter list, but is not a supported keyword argument for PartialUser.fetch_moderators(). rather, it's (helpfully) pulled directly from the object internal to the method

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
  • I have updated the changelog with a quick recap of my changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)
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[chillymosh]

Thanks