Builder: remove item from singleton registry

https://fedorahosted.org/freeipa/ticket/3235

install/ui/src/freeipa/_base/Singleton_registry.js

@@ -77,6 +77,17 @@ define(['dojo/_base/declare',
             return obj;
         },
 
+        /**
+         * Removes object of given type from registry
+         *
+         * @param {String} type
+         */
+        remove: function(type) {
+
+            var undefined;
+            this._map[type] = undefined;
+        },
+
         /**
          * Registers construction specification
          *
@@ -93,6 +104,7 @@ define(['dojo/_base/declare',
                     context: this
                 };
             }
+
             this.builder.registry.register(type, func, default_spec);
         },