Remove outdated comment.

All nonterminals collect and store tokens now. (Unless they are very
simple, e.g. single-token, and can precisely recover them without
collecting.)

compiler/rustc_parse/src/parser/nonterminal.rs

@@ -101,8 +101,6 @@ fn may_be_ident(nt: &token::Nonterminal) -> bool {
     /// site.
     #[inline]
     pub fn parse_nonterminal(&mut self, kind: NonterminalKind) -> PResult<'a, NtOrTt> {
-        // Any `Nonterminal` which stores its tokens (currently `NtItem` and `NtExpr`)
-        // needs to have them force-captured here.
         // A `macro_rules!` invocation may pass a captured item/expr to a proc-macro,
         // which requires having captured tokens available. Since we cannot determine
         // in advance whether or not a proc-macro will be (transitively) invoked,