How to use the cfgv.remove_defaults function in cfgv

# It's possible we didn't identify the rev lines in the original
            if not rev_line_indices_reversed:
                break
            line_index = rev_line_indices_reversed.pop()
            original_line = lines[line_index]
            orig_match = REV_LINE_RE.match(original_line)
            new_match = REV_LINE_RE.match(line)
            lines[line_index] = REV_LINE_FMT.format(
                orig_match.group(1), orig_match.group(2),
                new_match.group(3), orig_match.group(4),
            )

    # If we failed to intelligently rewrite the rev lines, fall back to the
    # pretty-formatted yaml output
    to_write = ''.join(lines)
    if remove_defaults(ordered_load(to_write), CONFIG_SCHEMA) != output:
        to_write = new_contents

    with open(path, 'w') as f:
        f.write(to_write)

def _write_new_config_file(path, output):
    with open(path) as f:
        original_contents = f.read()
    output = remove_defaults(output, CONFIG_SCHEMA)
    new_contents = ordered_dump(output, **C.YAML_DUMP_KWARGS)

    lines = original_contents.splitlines(True)
    rev_line_indices_reversed = list(
        reversed([
            i for i, line in enumerate(lines) if REV_LINE_RE.match(line)
        ]),
    )

    for line in new_contents.splitlines(True):
        if REV_LINE_RE.match(line):
            # It's possible we didn't identify the rev lines in the original
            if not rev_line_indices_reversed:
                break
            line_index = rev_line_indices_reversed.pop()
            original_line = lines[line_index]