REORG: h1: move legacy http functions to http_msg.c

REORG: h1: move legacy http functions to http_msg.c

Now that h1 and legacy HTTP are two distinct things, there's no need
to keep the legacy HTTP parsers in h1.c since they're only used by
the legacy code in proto_http.c, and h1.h doesn't need to include
hdr_idx anymore. This concerns the following functions :

- http_parse_reqline();
- http_parse_stsline();
- http_msg_analyzer();
- http_forward_trailers();

All of these were moved to http_msg.c.