Filter out strings that should not show up in the diff.

def _normalize_compare_config(self, diff):
        """Filter out strings that should not show up in the diff."""
        ignore_strings = [
            "Contextual Config Diffs",
            "No changes were found",
            "ntp clock-period",
        ]
        if self.auto_file_prompt:
            ignore_strings.append("file prompt quiet")

        new_list = []
        for line in diff.splitlines():
            for ignore in ignore_strings:
                if ignore in line:
                    break
            else:  # nobreak
                new_list.append(line)
        return "\n".join(new_list)