Revert "proxy.cgi: Fix for Bug #12826 'squid >=5 crashes on literal IPv6 addresses'"

Revert "proxy.cgi: Fix for Bug #12826 'squid >=5 crashes on literal IPv6 addresses'"

This reverts commit e0be9eab47d621545e5498c32c0fef39f7ef84a9.

This change is now producing problems on IPv6-enabled systems as it will
deny access to any website that is IPv6-enabled as well, even if the
client connected using IPv4.

I have tested if squid is now running on fine on systems where IPv6 is
disabled and can confirm that its running just fine.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
Acked-by: Peter Müller <peter.mueller@ipfire.org>