Use eslint for everything

eslint is much more powerful and flexible than jshint, and we don't want
to promote writing new projects with pre-ES6 code.

As a side effect, this also avoids downloading PhantomJS (see
https://github.com/jshint/jshint/issues/3318), thereby cutting down
node_modules/ from 470 MB to 210 MB.

package.json

@@ -24,8 +24,6 @@
     "extract-text-webpack-plugin": "^2.1.0",
     "htmlparser": "^1.7.7",
     "jed": "^1.1.1",
-    "jshint": "~2.9.1",
-    "jshint-loader": "~0.8.3",
     "po2json": "^0.4.5",
     "sass-loader": "^7.0.3",
     "sizzle": "^2.3.3",

src/app.jsx

@@ -1,4 +1,3 @@
-/*jshint esversion: 6 */
 /*
  * This file is part of Cockpit.
  *

src/index.es6

@@ -1,4 +1,3 @@
-/*jshint esversion: 6 */
 /*
  * This file is part of Cockpit.
  *

webpack.config.js

@@ -119,12 +119,6 @@ module.exports = {
     },
     module: {
         rules: [
-            {
-                enforce: 'pre',
-                exclude: /node_modules/,
-                loader: 'jshint-loader',
-                test: /\.js$/
-            },
             {
                 enforce: 'pre',
                 exclude: /node_modules/,
@@ -134,7 +128,7 @@ module.exports = {
             {
                 enforce: 'pre',
                 exclude: /node_modules/,
-                loader: 'jshint-loader?esversion=6',
+                loader: 'eslint-loader',
                 test: /\.es6$/
             },
             {