ipn/ipnlocal: strip origin and referer headers from Taildrive requests

peerapi does not want these, but rclone includes them.
Stripping them out allows rclone to work with Taildrive configured
as a WebDAV remote.

Updates #cleanup

Signed-off-by: Percy Wegmann <percy@tailscale.com>

ipn/ipnlocal/local.go

@@ -4833,6 +4833,10 @@ func (dt *driveTransport) RoundTrip(req *http.Request) (resp *http.Response, err
 		req.Body = bw
 	}
 
+	// Strip origin and referer headers
+	req.Header.Del("origin")
+	req.Header.Del("referer")
+
 	defer func() {
 		contentType := "unknown"
 		switch req.Method {