Bug 25950: Remove <client> in X-Forwarded-For from proxy tests

Bug 25950: Remove <client> in X-Forwarded-For from proxy tests

This patch removes the <client> ip address in the X-Forwarded-For
header from being tested against koha_trusted_proxies.

Without this patch, REMOTE_ADDR will be set to null, if the <client>
ip address matches against koha_trusted_proxies.

To Test:
1. Run the unit test t/Koha/Middleware/RealIP.t

Signed-off-by: Didier Gautheron <didier.gautheron@biblibre.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>