gateway: remove Suborigins as it conflicts the spec

The Suborigins spec was changed and we have to adjust, the spec is still
unstable and it might change in future. Currently the only browser
supporting it (Chrome) errors out on it as it doesn't confront spec it
uses.

See ipfs/specs#131

License: MIT
Signed-off-by: Jakub Sztandera <kubuxu@protonmail.ch>

core/corehttp/gateway_handler.go

@@ -199,19 +199,6 @@ func (i *gatewayHandler) getOrHeadHandler(ctx context.Context, w http.ResponseWr
 	// expose those headers
 	w.Header().Set("Access-Control-Expose-Headers", "X-Stream-Output, X-Chunked-Output")
 
-	// Suborigin header, sandboxes apps from each other in the browser (even
-	// though they are served from the same gateway domain).
-	//
-	// Omited if the path was treated by IPNSHostnameOption(), for example
-	// a request for http://example.net/ would be changed to /ipns/example.net/,
-	// which would turn into an incorrect Suborigin: example.net header.
-	//
-	// NOTE: This is not yet widely supported by browsers.
-	if !ipnsHostname {
-		pathRoot := strings.SplitN(urlPath, "/", 4)[2]
-		w.Header().Set("Suborigin", pathRoot)
-	}
-
 	// set these headers _after_ the error, for we may just not have it
 	// and dont want the client to cache a 500 response...
 	// and only if it's /ipfs!