CLEANUP: mux-h2: Remove the h1 parser state from the h2 stream

CLEANUP: mux-h2: Remove the h1 parser state from the h2 stream

Since the h2 multiplexer no longer relies on the legacy HTTP representation, and
uses exclusively the HTX, the H1 parser state (h1m) is no longer used by the h2
streams. Thus it can be removed.

This patch may be backported as far as 2.1.

(cherry picked from commit fafd1b0a5b3b6ee0c7d7dd288629c992fc63ef10)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit aa3c7001cb32cd9c5bb7b5258459bb971e956438)
[wt: include file is in common/h1.h in 2.1]
Signed-off-by: Willy Tarreau <w@1wt.eu>