Remove never-supported WebRTC APIs

[saschanaz]

A checklist to help your pull request get merged faster:

• Summarize your changes
• Data: link to resources that verify support information (such as browser's docs, changelogs, source control, bug trackers, and tests)
• Data: if you tested something, describe how you tested with details like browser and version
• Review the results of the linter and fix problems reported (If you need help, please ask in a comment!)
• Link to related issues or pull requests, if any: Remove items that has never been supported #6854, Remove totally unimplemented things #6768

[queengooborg]

Looks good to me, thanks!

[ddbeck]

This PR shares problems around page removals/redirects like some of the other recent feature removal PRs. I was going to start cleaning the pages up, but on closer examination, I think the data is not trustworthy enough to merit removal on its own (e.g., https://chromestatus.com/feature/5085886951718912 shows at least some of the RTCIceTransport API is supported in Chrome; the current data is all false).

I'm going to revert this, but if you want to reopen this as a new PR or issue and explore the data here more thoroughly, that would be fine. I'm not rejecting this PR so much as declaring it premature.

[ddbeck]

Reverted with #7414.