Drop third party webpack-chunk-hash

We noticed irregular behavior in the hashing of our ubndled auspice
files [1]. The webpack-chunk-hash (a.k.a. WebpackChunkHash) library
appears to have been abandoned by its developers with no commits in the
past 4 years. I'm not sure what purpose this library originally served,
but after taking a hint from Ivan, it appears that Webpack natively does
exactly what we want with respect to chunk hashing and content hashing.

Therefore, drop the third party webpack-chunk-hash library from our
webpack config in favor of the vanilla webpack API.

[1]: #1266

package.json

@@ -124,7 +124,6 @@
     "typeface-lato": "^0.0.75",
     "webpack": "^4.30.0",
     "webpack-bundle-analyzer": "^3.3.2",
-    "webpack-chunk-hash": "^0.6.0",
     "webpack-cli": "^3.1.2",
     "webpack-dev-middleware": "^3.1.3",
     "webpack-hot-middleware": "^2.24.3",

webpack.config.js

@@ -6,7 +6,6 @@ const fs = require('fs');
 const utils = require('./cli/utils');
 const HtmlWebpackPlugin = require('html-webpack-plugin');
 const { CleanWebpackPlugin } = require('clean-webpack-plugin');
-const WebpackChunkHash = require('webpack-chunk-hash');
 const LodashModuleReplacementPlugin = require('lodash-webpack-plugin');
 
 /* Webpack config generator */
@@ -97,7 +96,6 @@ const generateConfig = ({extensionPath, devMode=false, customOutputPath, analyze
   ] : [
     new LodashModuleReplacementPlugin(),
     pluginProcessEnvData,
-    new WebpackChunkHash({algorithm: 'md5'}),
     pluginCompress,
     pluginHtml,
     cleanWebpackPlugin