Update Onion-Location in tor-browser-spec

In legacy/trac#21952 (moved) I updated the onion-location spec (https://github.com/acatarineu/torspec/blob/21952+1/proposals/ideas/onion-location.txt) based on https://gitweb.torproject.org/user/asn/torspec.git/commit/?h=onion-location&id=14fc750e3afcd759f4235ab955535a07eed24286. I did not realize that this was already in the tor-browser-spec repo: https://gitweb.torproject.org/tor-browser-spec.git/tree/proposals/100-onion-location-header.txt.

In any case, I think we should update that spec in the upstream tor-browser-spec repo.