BUILD: peers: fix build warning about unused variable

BUILD: peers: fix build warning about unused variable

Previous commit da2b0844f ("MINOR: peers: Add traces for peer control
messages.") introduced a build warning on some compiler versions after
the removal of variable "peers" in peer_send_msgs() because variable
"s" was used only to assign this one, and variable "si" to assign "s".
Let's remove both to fix the warning. No backport is needed.

(cherry picked from commit 81d7092dbd25db04cc72d2dca77647d548342256)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>