remove WRAPPED_OPTIONS once loaded

This makes reentrant ikiwiki calls from wrappers work.

ikiwiki.in

@@ -105,6 +105,7 @@ sub getconfig () { #{{{
 		if ($@) {
 			error("WRAPPED_OPTIONS: $@");
 		}
+		delete $ENV{WRAPPED_OPTIONS};
 		loadplugins();
 		checkconfig();
 	}