Remove the old implementation of comparing headlines.

src/compare/util.rs

@@ -221,22 +221,6 @@ pub(crate) fn get_property_quoted_string<'b, 's, 'x>(
         .map_or(Ok(None), |r| r.map(Some))?)
 }
 
-/// Get a named property containing a boolean value.
-///
-/// This uses the elisp convention of nil == false, non-nil == true.
-///
-/// Returns false if key is not found.
-pub(crate) fn get_property_boolean<'b, 's, 'x>(
-    emacs: &'b Token<'s>,
-    key: &'x str,
-) -> Result<bool, Box<dyn std::error::Error>> {
-    Ok(get_property(emacs, key)?
-        .map(Token::as_atom)
-        .map_or(Ok(None), |r| r.map(Some))?
-        .unwrap_or("nil")
-        != "nil")
-}
-
 /// Get a named property containing an unquoted numeric value.
 ///
 /// Returns None if key is not found.