RFE: move away from deprecated html5lib

[kloczek]

Is your feature request related to a problem? Please describe.
It would be nice tu cut tail of some legacy modules decencies.
One of those modules is html5lib.

Describe the solution you'd like
it wold be good to remove use od=f the html5lib deprecated html5lib like it has been done with pip ~2 years ago.
pypa/pip#11259

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
html5lib depends on six which is on list of deprecated modules even longer implanting this RFE would make easier kill two birds using one stone 😋

[nicholascar]

I support this idea of moving away from html5lib. @kloczek please do make a PR for this!