Follow up issue for respec error using WEB IDL partial namespace

[relu91]

I created https://github.com/w3c/respec/issues/4447, maybe there is a simple solution/fix for it.

Originally posted by @danielpeintner in #477 (comment)

Also look at this comment: #477 (comment)

[danielpeintner]

Keep open until https://github.com/w3c/respec/issues/4447 has been fixed. Once fixed we can partly remove things from #518 (remove script and step 5)