[scraper] use the document API to get raw content

[wbamberg]

Currently the scraper gets:

• pre-macro content from: https://wiki.developer.mozilla.org/en-US/docs/Web/HTML/Element/progress?raw
• post-macro content from: https://wiki.developer.mozilla.org/en-US/docs/Web/HTML/Element/progress?raw&macros

But both are available from https://developer.mozilla.org/api/v1/doc/en-US/Web/HTML/Element/progress . So we should use that instead.

[peterbe]

It also means we can drop things like removeNode(dom, 'section.Quick_links');