This allows us to separate the zilencer paths from other JSON paths,
with explicit type annotation expecting `RemoteZulipServer` as the
second parameter of the handler using
authenticated_remote_server_view.
The test case is also updated to remove a test for a situation that no
longer occurs anymore, since we don't perform subdomain checks on
remote servers.
Signed-off-by: Zixuan James Li <p359101898@gmail.com>