Remove TokenTreeCursor::replace_prev_and_rewind.

It's no longer used.

Author: nnethercote

compiler/rustc_ast/src/tokenstream.rs

@@ -714,15 +714,6 @@ impl TokenTreeCursor {
  pub fn look_ahead(&self, n: usize) -> Option<&TokenTree> {
  self.stream.0.get(self.index + n)
  }
-
- // Replace the previously obtained token tree with `tts`, and rewind to
- // just before them.
- pub fn replace_prev_and_rewind(&mut self, tts: Vec<TokenTree>) {
- assert!(self.index > 0);
- self.index -= 1;
- let stream = Lrc::make_mut(&mut self.stream.0);
- stream.splice(self.index..self.index + 1, tts);
- }
 }
 
 #[derive(Debug, Copy, Clone, PartialEq, Encodable, Decodable, HashStable_Generic)]