Remove unnnecessary polyfills from test environment

These are no longer needed when running tests under Chrome.

src/karma.config.js

@@ -40,14 +40,6 @@ module.exports = function(config) {
 
     // list of files / patterns to load in the browser
     files: [
-      // Polyfills for PhantomJS
-      './shared/polyfills/es2015.js',
-      './shared/polyfills/es2016.js',
-      './shared/polyfills/es2017.js',
-      './shared/polyfills/string.prototype.normalize.js',
-      './shared/polyfills/fetch.js',
-      './shared/polyfills/url.js',
-
       // Test setup
       './sidebar/test/bootstrap.js',