message: Remove useless copies of `labels` in `rename`.
  These new bindings were unecessary. Leftover from when renaming used a separate arena?
diff: @@ -611,13 +611,11 @@ impl<'arena, 'env> Context<'arena, 'env> {
  }
  Value::RecordType(labels, types) => {
  - let labels = self.scope.to_scope(labels); // FIXME: avoid copy if this is the same arena?
  let types = self.rename_telescope(meta_var, types)?;
  Ok(Term::RecordType(span, labels, types))
  }
  Value::RecordLit(labels, exprs) => {
  - let labels = self.scope.to_scope(labels); // FIXME: avoid copy if this is the same arena?
  let mut new_exprs = SliceVec::new(self.scope, exprs.len());
  for expr in exprs {
  new_exprs.push(self.rename(meta_var, expr)?);
  @@ -636,7 +634,6 @@ impl<'arena, 'env> Context<'arena, 'env> {
  }
  Value::FormatRecord(labels, formats) => {
  - let labels = self.scope.to_scope(labels); // FIXME: avoid copy if this is the same arena?
  let formats = self.rename_telescope(meta_var, formats)?;
  Ok(Term::FormatRecord(span, labels, formats))
  @@ -652,7 +649,6 @@ impl<'arena, 'env> Context<'arena, 'env> {
  ))
  }
  Value::FormatOverlap(labels, formats) => {
  - let labels = self.scope.to_scope(labels); // FIXME: avoid copy if this is the same arena?
  let formats = self.rename_telescope(meta_var, formats)?;
  Ok(Term::FormatOverlap(span, labels, formats))
  