Remove license comments from the UMD build (#1437)

* Install terser plugin explicite to enable extensive customization

* Remove license comment from the UMD builds using string-replace-loader webpack plugin

* Test for the redundant license comments in the UMD build inside the verify:umd script

.config/webpack/base.js

@@ -2,6 +2,7 @@ const path = require('path');
 const fs = require('fs');
 const { BannerPlugin } = require('webpack');
 
+const licenseComment = fs.readFileSync(path.resolve(__dirname, '../source-license-header.js'), 'utf8').trim();
 let licensePreamble = fs.readFileSync(path.resolve(__dirname, '../../LICENSE.txt'), 'utf8');
 
 licensePreamble += '\n\nVersion: ' + process.env.HT_VERSION;
@@ -42,6 +43,14 @@ module.exports.create = function create(processedFile) {
             }
           ]
         },
+        {
+          test: /\.js$/,
+          loader: 'string-replace-loader',
+          options: {
+            search: licenseComment,
+            replace: '',
+          }
+        }
       ]
     },
     plugins: [