Empty docs for let_underscore_drop

[frederikhors]

Description

There is nothing in https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_drop ?

[koka831]

It seems let_underscore_drop lint is moved into rustc in rust-lang/rust#97739,
so we can find its document in https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#let-underscore-drop .

[frewsxcv]

This can be closed