Remove comment fetcher

(See also microsoft#1097 (comment))

Both fetch-comment and fetch-mdn are not being maintained and are currently broken.

Theoretically we can fetch markdown text from https://github.com/mdn/content/tree/main/files/en-us/web/api/ but that needs some real interest, which I doubt anyone has.

Author: saschanaz