BUG/MINOR: h1: don't consider the status for each header

BUG/MINOR: h1: don't consider the status for each header

While it was possible to consider the status before parsing response
headers, it's wrong to do it for request headers and could lead to
random behaviours due to this status matching other fields instead.
Additionnally there is little to no value in doing this for each and
every new header field. It's much better to reset the content-length
at once in the callerwhen seeing such statuses (which currently is only
the H2 mux).

No backport is needed, this is purely 1.9.