maint: Remove plugin-transform-optional-chaining from babel.

The optional chaining feature is already included in preset-env ES2020.

Author: thet

babel.config.js

@@ -26,7 +26,6 @@ module.exports = (env) => {
                     },
                 ],
             ],
-            plugins: ["@babel/plugin-transform-optional-chaining"],
         };
     }