use an appropriate value for network.http.sendOriginHeader

From #33534 (closed): In Firefox 70, the network.http.sendOriginHeader pref value was changed from 0 (never send Origin header) to 2 (always send). What value should Tor Browser use?

https://bugzilla.mozilla.org/show_bug.cgi?id=1424076
"Enable network.http.sendOriginHeader by default"