Make sure telemetry reporting is disabled in Tor Browser 9

We explicitly unset telemetry reporting for mobile and have this disabled for desktop as well.

We should double-check this for Tor Browser 9, though, as MOZ_TELEMETRY_REPORTING gets now automatically set for builds using official settings (as we do), see https://bugzilla.mozilla.org/show_bug.cgi?id=1549886.