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.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index aa0a760..740e255 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -14,7 +14,6 @@
 #include <haproxy/api.h>
 #include <haproxy/cfgparse.h>
 #include <haproxy/connection.h>
-#include <haproxy/h1.h>
 #include <haproxy/h2.h>
 #include <haproxy/hpack-dec.h>
 #include <haproxy/hpack-enc.h>
@@ -192,13 +191,12 @@
 
 
 /* H2 stream descriptor, describing the stream as it appears in the H2C, and as
- * it is being processed in the internal HTTP representation (H1 for now).
+ * it is being processed in the internal HTTP representation (HTX).
  */
 struct h2s {
 	struct conn_stream *cs;
 	struct session *sess;
 	struct h2c *h2c;
-	struct h1m h1m;         /* request or response parser state for H1 */
 	struct eb32_node by_id; /* place in h2c's streams_by_id */
 	int32_t id; /* stream ID */
 	uint32_t flags;      /* H2_SF_* */
@@ -1438,16 +1436,6 @@
 	h2s->body_len  = 0;
 	h2s->rxbuf     = BUF_NULL;
 
-	if (h2c->flags & H2_CF_IS_BACK) {
-		h1m_init_req(&h2s->h1m);
-		h2s->h1m.err_pos = -1; // don't care about errors on the request path
-		h2s->h1m.flags |= H1_MF_TOLOWER;
-	} else {
-		h1m_init_res(&h2s->h1m);
-		h2s->h1m.err_pos = -1; // don't care about errors on the response path
-		h2s->h1m.flags |= H1_MF_TOLOWER;
-	}
-
 	h2s->by_id.key = h2s->id = id;
 	if (id > 0)
 		h2c->max_id      = id;