align devServer definition with #26895 by removing it in v3 also (#27287)

types/webpack/v3/index.d.ts

@@ -85,8 +85,6 @@ declare namespace webpack {
         watchOptions?: Options.WatchOptions;
         /** Switch loaders to debug mode. */
         debug?: boolean;
-        /** Can be used to configure the behaviour of webpack-dev-server when the webpack config is passed to webpack-dev-server CLI. */
-        devServer?: any; // TODO: Type this
         /** Include polyfills or mocks for various node stuff */
         node?: Node | false;
         /** Set the value of require.amd and define.amd. */