ChromeWebrtcIpLeakageTest fails with Chromium 76

[mike10004]

This test is now failing due to a Javascript error, and the root cause appears to be that the behavior that the script expects, that a particular object with relevant IP address properties, a member of the WebRTC connection instance, is no longer the actual behavior, which is that the member is null.

However, rather than fixing the script that the test uses, the local IP leak protection should instead be removed as a feature, because both Chrome/Chromium and Firefox now provide methods to disable WebRTC or protect the local IP.

For Firefox, setting media.peerconnection.enabled to false disables WebRTC, and in Chrome/Chromium, the flag enable-webrtc-hide-local-ips-with-mdns can be set, according to https://bugs.chromium.org/p/chromium/issues/detail?id=333752#c112.