atomic::Ordering: Get rid of misleading parts of intro
atomic::Ordering: Get rid of misleading parts of intro

Remove the parts of atomic::Ordering's intro that wrongly claimed that
SeqCst prevents all reorderings around it.

Closes #55196

GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust