relicense shootout-regex-dna.rs

Part of #14248

The authors are @pcwalton and @BurntSushi, and we have their agreement.
Add visit_attribute to Visitor, use it for unused_attribute

The lint was missing a *lot* of cases previously.
Remove the attribute_usage lint

It has been superseded by the unused_attribute lint.

[breaking change]
Add back hint for crate level attributes
Remove unused name_str_pair method
std::io: expand the oneshot/periodic docs.

Examples!

Fixes #14714.
auto merge of #14728 : TeXitoi/rust/relicense-shootout-regex-dna, r=brson

Part of #14248

The authors are @pcwalton and @BurntSushi, and we have their agreement.

@brson OK?
auto merge of #14741 : sfackler/rust/visit-attr, r=alexcrichton

The lint was missing a *lot* of cases previously.
auto merge of #14745 : huonw/rust/timer-doc, r=alexcrichton

std::io: expand the oneshot/periodic docs.

Examples!

Fixes #14714.
Fix an LLVM assertion when matching against static strings

Fixes #8315
Fixes #11940