BUG/MINOR: cfgparse: do not mention "addr:port" as supported on proxy lines

BUG/MINOR: cfgparse: do not mention "addr:port" as supported on proxy lines

The very old error message indicating that a proxy name is mandatory
still had a reference to the optional addr:port argument while this one
is explicitly rejected a few lines later since at least 1.9.

This is harmless but confusing. This can be backported to 2.0.

(cherry picked from commit b2ec994523067bc03c0e631e4f5d4ba8dae02cb9)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit a3201bc5dbf5a837cbd9c25d0c795868f236871a)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 0ca103d643981c935f0c64eb5995be4d15a646d8)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>