GVST is how these probes sent data in Fenix and is now unnecessary (and doesn't send data in Fenix release) since Firefox Desktop has direct access to Glean. We therefore need to clean them up in some capacity.
Following the recommendations from the GeckoView Streaming (GVST) validation effort, this is a pure Glean api implementation of the metrics that fell under network in geckoview streaming.
Because these were all categorical histograms, to retain previous functionality we've added parallel instrumentation in Glean.
Differential Revision: https://phabricator.services.mozilla.com/D201024
