Auto merge of #32909 - sanxiyn:unused-trait-import-2, r=alexcrichton

Remove unused trait imports

src/libsyntax/parse/parser.rs

@@ -59,7 +59,6 @@ use ptr::P;
 use parse::PResult;
 
 use std::collections::HashSet;
-use std::io::prelude::*;
 use std::mem;
 use std::path::{Path, PathBuf};
 use std::rc::Rc;