Macro rustc_feature::removed::declare_features

macro_rules! declare_features {
    ($($(#[doc = $doc : tt]) *
   (removed, $feature : ident, $ver : expr, $issue : expr, None, $reason :
    expr),) +) => { ... };
    ($($(#[doc = $doc : tt]) *
   (stable_removed, $feature : ident, $ver : expr, $issue : expr, None),) +) => { ... };
}