eyre: use 303 to redirect to login post-logout

This ensures the client sends a GET request, which is more appropriate.

pkg/arvo/sys/vane/eyre.hoon

@@ -1012,7 +1012,7 @@
       ::
       =/  response=$>(%start http-event:http)
         :*  %start
-            response-header=[307 ['location' '/~/login']~]
+            response-header=[303 ['location' '/~/login']~]
             data=~
             complete=%.y
         ==