Remove unnecessary babel transform plugins from babel-preset-react-app

The `babel-plugin-transform-object-rest-spread` v6.19.0 update makes
these plugins unnecessary, as v6.19.0 can be used stand-alone

packages/babel-preset-react-app/index.js

@@ -27,15 +27,7 @@ const plugins = [
       regenerator: true,
       // Resolve the Babel runtime relative to the config.
       moduleName: path.dirname(require.resolve('babel-runtime/package'))
-    }],
-    // The following two plugins are currently necessary to get
-    // babel-preset-env to work with rest/spread. More info here:
-    // https://github.com/babel/babel-preset-env#caveats
-    // https://github.com/babel/babel/issues/4074
-    // const { a, ...z } = obj;
-    require.resolve('babel-plugin-transform-es2015-destructuring'),
-    // const fn = ({ a, ...otherProps }) => otherProps;
-    require.resolve('babel-plugin-transform-es2015-parameters')
+    }]
   ];
 
 // This is similar to how `env` works in Babel:

packages/babel-preset-react-app/package.json

@@ -12,8 +12,6 @@
   ],
   "dependencies": {
     "babel-plugin-transform-class-properties": "6.16.0",
-    "babel-plugin-transform-es2015-destructuring": "6.16.0",
-    "babel-plugin-transform-es2015-parameters": "6.17.0",
     "babel-plugin-transform-object-rest-spread": "6.19.0",
     "babel-plugin-transform-react-constant-elements": "6.9.1",
     "babel-plugin-transform-react-jsx-self": "6.11.0",