drop build:css stage

packages/controls/css/widgets.css

@@ -2,9 +2,5 @@
  * Distributed under the terms of the Modified BSD License.
  */
 
- /* We import all of these together in a single css file because the Webpack
-loader sees only one file at a time. This allows postcss to see the variable
-definitions when they are used. */
-
 @import "./labvariables.css";
 @import "./widgets-base.css";

packages/controls/package.json

@@ -17,8 +17,7 @@
     "url": "https://github.com/jupyter-widgets/ipywidgets.git"
   },
   "scripts": {
-    "build": "npm run build:src && npm run build:css",
-    "build:css": "postcss --use postcss-import --use postcss-cssnext -o css/widgets.built.css css/widgets.css",
+    "build": "npm run build:src",
     "build:src": "tsc --project src",
     "build:test": "tsc --project test/src && webpack --config test/webpack.conf.js",
     "clean": "npm run clean:src",
@@ -67,10 +66,6 @@
     "karma-webpack": "^2.0.3",
     "mocha": "^3.3.0",
     "npm-run-all": "^1.5.1",
-    "postcss-cli": "^4.1.0",
-    "postcss-cssnext": "^3.0.2",
-    "postcss-import": "^10.0.0",
-    "postcss-loader": "^2.0.6",
     "rimraf": "^2.6.1",
     "sinon": "^2.1.0",
     "sinon-chai": "^2.11.0",