fix ap_remove_output_filter; the recent change to use remove_any_filter made

it possible to wipe out the entire filter chain.  and then when
ap_finalize_request_protocol was called, r->output_filters was NULL,
preventing data from being flushed to the client.
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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90801 13f79535-47bb-0310-9956-ffa450edef68