After looking a bit at it it seemed Mozilla did not get to it until the 48 timeline (https://bugzilla.mozilla.org/show_bug.cgi?id=1254752). But after landing these changes they seemed to have resurrected the APIs. Thus, definitely nothing we need to care about while preparing for ESR 45. Putting that on the ESR 52 radar.
Trac: Summary: The newChannel() API is deprecated and broken in Tor Browser based on ESR 45 to The newChannel() API is deprecated and broken in Tor Browser based on ESR 52 Keywords: tbb-6.0a5, ff45-esr, GeorgKoppen201604, TorBrowserTeam201604 deleted, ff52-esr added
Trac: Summary: The newChannel() API is deprecated and broken in Tor Browser based on ESR 52 to The newChannel() API is deprecated and broken in Tor Browser based on ESR 59
Trac: Summary: The newChannel() API is deprecated and broken in Tor Browser based on ESR 59 to The newChannel() API is deprecated and broken in Tor Browser based on ESR 60