http: remove unnecessary _prev_body logic
http: remove unnecessary _prev_body logic

It is up to the user to make sure request bodies are fully read (in the
WSGI handler server-side, or as a user of HttpClient client-side).  The
request pipeline can stall if this is not done. This code was not doing
anything to prevent that.

geertj/gruvi,swegener/gruvi,swegener/gruvi,geertj/gruvi