Remove the api.CharacterData.ChildNode entry (#8052)
Remove the api.CharacterData.ChildNode entry (#8052)

ChildNode is a mixin, not an interface as described, and mixins are
completely invisible to web developers; they're a spec author
convenience.

This is a bit of cleanup that makes sense regardless of the outcome of
https://github.com/mdn/browser-compat-data/issues/472 more broadly.
mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data