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Rollup merge of #153401 - GuillaumeGomez:migrate-diag, r=JonathanBrouwer
Migrationg of `LintDiagnostic` - part 7
Part of https://github.com/rust-lang/rust/issues/153099.
This PR removes the `LintDiagnostic` trait and proc-macro. \o/
r? @JonathanBrouwer