duplicheck: Remove confusing plugin

This plugin was developed for a customer who had very specific
requirements.  It never did anything useful for regular users and
usually caused confusing errors if they enabled it by mistake.  So
just remove it.

conf/Makefile.am

@@ -41,7 +41,6 @@ plugins = \
 	plugins/dhcp.opt \
 	plugins/dnscert.opt \
 	plugins/drbg.opt \
-	plugins/duplicheck.opt \
 	plugins/eap-aka.opt \
 	plugins/eap-aka-3gpp.opt \
 	plugins/eap-aka-3gpp2.opt \

conf/plugins/duplicheck.opt

@@ -1,5 +0,0 @@
-charon.plugins.duplicheck.enable = yes
-	Enable duplicheck plugin (if loaded).
-
-charon.plugins.duplicheck.socket = unix://${piddir}/charon.dck
-	Socket provided by the duplicheck plugin.