MEDIUM: filters: remove http_start_chunk, http_last_chunk and http_chunk_end

MEDIUM: filters: remove http_start_chunk, http_last_chunk and http_chunk_end

For Chunked HTTP request/response, the body filtering can be really
expensive. In the worse case (many chunks of 1 bytes), the filters overhead is
of 3 calls per chunk. If http_data callback is useful, others are just
informative.

So these callbacks has been removed. Of course, existing filters (trace and
compression) has beeen updated accordingly. For the HTTP compression filter, the
update is quite huge. Its implementation is closer to the old one.