Rollup merge of #116019 - dtolnay:percratesearch, r=GuillaumeGomez

Delete obsolete `--disable-per-crate-search` rustdoc flag

This unstable flag is unused by rustdoc since rust-lang/rust@ef96d57.

We should avoid landing this until after rust-lang/docs.rs#2225 is deployed to docs.rs.

Author: GuillaumeGomez