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),
    )+) => { ... };
}