Disabling autoprefixer in css-loader, explicitly using postcss-loader (#9904)

Backports PR #9899

**Commit 1:**
Disabling autoprefixer in css-loader, explicitly using postcss-loader

* Original sha: 575d50ac4f
* Authored by kobelb <brandon.kobel@elastic.co> on 2017-01-16T22:26:06Z

src/optimize/base_optimizer.js

@@ -71,18 +71,18 @@ class BaseOptimizer {
 
     const makeStyleLoader = preprocessor => {
       let loaders = [
-        loaderWithSourceMaps('css-loader')
+        loaderWithSourceMaps('css-loader?autoprefixer=false'),
+        {
+          name: 'postcss-loader',
+          query: {
+            config: require.resolve('./postcss.config')
+          }
+        },
       ];
 
       if (preprocessor) {
         loaders = [
           ...loaders,
-          {
-            name: 'postcss-loader',
-            query: {
-              config: require.resolve('./postcss.config')
-            }
-          },
           loaderWithSourceMaps(preprocessor)
         ];
       }