WebRx: remove leftovers from grunt setup

We removed the gruntfile but forgot to edit `.gitignore` and `package.json`

Ref https://github.com/tastejs/todomvc/commit/adc4c72a370c5ce7c54aeead365f7559a447935b

examples/webrx/.gitignore

-node_modules/grunt
-node_modules/grunt-contrib-connect
-
 node_modules/rx/*
 node_modules/rx/dist/*
 !node_modules/rx/dist

examples/webrx/package.json

 {
   "private": true,
-  "devDependencies": {
-    "grunt": "^0.4.5",
-    "grunt-contrib-connect": "^0.9.0"
-  },
   "dependencies": {
     "rx": "~2.5.2",
     "todomvc-app-css": "^1.0.0",