Remove option to disable ipv6

It has been default for a while, is the only tested option,
and will only get more common.

win32/config.h.tt

@@ -2,7 +2,6 @@
 #define ENABLE_NLS
 #define USE_PLUGIN
 #define USE_OPENSSL
-#define USE_IPV6
 #define HAVE_ISO_CODES
 #define ISO_CODES_PREFIX ".\\"
 #define ISO_CODES_LOCALEDIR LOCALEDIR
@@ -13,6 +12,3 @@
 #define OLD_PERL
 #define GETTEXT_PACKAGE "hexchat"
 #define PACKAGE_TARNAME "hexchat-<#= [string]::Join('.', $versionParts) #>"
-#ifndef USE_IPV6
-#define socklen_t int
-#endif