BUG/MINOR: stats: Don't state the 303 redirect response is chunked

BUG/MINOR: stats: Don't state the 303 redirect response is chunked

Start-line flags for 303-See-Other response returned by the stats applet are
not properly set. Indeed, the reponse has a "content-length" header but both
HTX_SL_F_CHNK and HTX_SL_F_CLEN flags are set. Because of this bug, the
reponse is considered as chunked. So, let's remove HTX_SL_F_CHNK flag.

And also add HTX_SL_F_BODYLESS flag because there is no payload
("content-length" header is always set to 0).

This patch must be backported to all stable versions. On the 2.8 and lower
versions, the commit d0b04920d1 ("BUG/MINOR: htpp-ana/stats: Specify that
HTX redirect messages have a C-L header") must be backported first.