Remove reference to deprecated image

The #20553 changed the deprecated hello-node image to echoserver image. However, there is a reference to the old image later in the text. Point 5 implies that there will be a 'Hello World' message. This probably was true for the hello-node image but the echoserver does not print this (it echoes back the request with all of its params). This may be misleading, so change the text to a generic 'app's response'/'sample app'. Unused JS sources of the old image are removed.

content/en/examples/minikube/Dockerfile

@@ -1,4 +0,0 @@
-FROM node:6.14.2
-EXPOSE 8080
-COPY server.js .
-CMD [ "node", "server.js" ]

content/en/examples/minikube/server.js

@@ -1,9 +0,0 @@
-var http = require('http');
-
-var handleRequest = function(request, response) {
-  console.log('Received request for URL: ' + request.url);
-  response.writeHead(200);
-  response.end('Hello World!');
-};
-var www = http.createServer(handleRequest);
-www.listen(8080);