Rollup merge of #153020 - GuillaumeGomez:improve-empty-impl-blocks-sentence, r=Urgau

rustdoc: Improve sentence for documented empty impl blocks

Part of rust-lang/rust#152874.

An impl block is not necessarily empty, so instead, better to precise that there are no **public** items.

r? @Urgau

Author: JonathanBrouwer