docs: remove dead link for `cross-publish-custom-rules`

[xuwei-k]

• https://github.com/scalacenter/scalafix/pull/1939
• https://github.com/scalacenter/scalafix/blob/112fd902227a9a90351af66761777997a9c793ba/docs/developers/local-rules.html#L229
• https://scalacenter.github.io/scalafix/docs/developers/local-rules.html

[bjaglin]

FTR, there is what seems to be a transient failure when publishing, so this update is not effective yet