Remove broken/deprecated mime.wasm property setter

Since `[email protected]`, the `mime.types` property has been deprecated and privatized. I also believe that this call is no longer needed in the new version.

Fixes webpack#1724

lib/Server.js

@@ -155,10 +155,6 @@ class Server {
     // eslint-disable-next-line
     const app = (this.app = new express());
 
-    // ref: https://github.com/webpack/webpack-dev-server/issues/1575
-    // remove this when send@^0.16.3
-    express.static.mime.types.wasm = 'application/wasm';
-
     app.all('*', (req, res, next) => {
       if (this.checkHost(req.headers)) {
         return next();