remove peek_span_src_raw from StringReader

src/librustc_save_analysis/span_utils.rs

@@ -53,7 +53,7 @@ impl<'a> SpanUtils<'a> {
     pub fn sub_span_of_token(&self, span: Span, tok: TokenKind) -> Option<Span> {
         let mut toks = self.retokenise_span(span);
         loop {
-            let next = toks.real_token();
+            let next = toks.next_token();
             if next == token::Eof {
                 return None;
             }