"unicode" does not exist on python3 and on python2 it was not needed
anymore here.

this is not used and cause a SyntaxWarning

- HTMLParseError no longer exist, on python3 parse_declaration throws
AttributeError

py2:
  https://github.com/python/cpython/blob/2.7/Lib/markupbase.py#L135-L140
  https://github.com/python/cpython/blob/2.7/Lib/HTMLParser.py#L124
py3:
  https://github.com/python/cpython/blob/3.12/Lib/_markupbase.py#L130-L134

- scrubHTML must pass `html` as unicode on python2 and str on python3,
adjust the check to cover both py2 / py3