remove useless handling of instanceOf and oneOf

There is no special treatment of `Proptypes.{instanceOf, oneOf}` types
so they might as well be handled as unrecognized types.

lib/util/propTypes.js

@@ -386,13 +386,6 @@ module.exports = function propTypesInstructions(context, components, utils) {
           }
           return unionTypeDefinition;
         }
-        case 'instanceOf':
-          return {
-            type: 'instance',
-            // Accept all children because we can't know what type they are
-            children: true
-          };
-        case 'oneOf':
         default:
           return {};
       }