Move the xml reporter away from the deprecated IReporter interface.

include/internal/catch_impl.hpp

@@ -88,8 +88,6 @@ namespace Catch {
     Matchers::Impl::StdString::EndsWith::~EndsWith() {}
 
     void Config::dummy() {}
-
-    INTERNAL_CATCH_REGISTER_LEGACY_REPORTER( "xml", XmlReporter )
 }
 
 #ifdef __clang__