Neuter NetworkInformation API on Tor Browser Mobile

The Networkinformation API is enabled by default in the mobile version of Firefox. This is governed by a preference, dom.netinfo.enabled. This API (https://developer.mozilla.org/en-US/docs/Web/API/NetworkInformation) provides a variety of information, e.g. the connection type a device is using to communicate with the network or the maximum downlink speed. We should avoid fingerprinting risks associated with this API. For a discussion among Mozilla engineers see: https://groups.google.com/forum/#!topic/mozilla.dev.platform/lCZmhCDGHPY