Drop authors entry from manifest

[lnicola]

• [x] I agree to follow the project's code of conduct.

• [x] I added an entry to CHANGELOG.md if knowledge of this change could be valuable to users.

This is soft-deprecated: https://rust-lang.github.io/rfcs/3052-optional-authors-field.html.

[lnicola]

bors r+

[bors[bot]]

Build succeeded!

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• ci result