Remove the now unneeded polyfills.

js/tests/karma.conf.js

@@ -137,16 +137,6 @@ if (browserStack) {
         branches: 89,
         functions: 90,
         lines: 90
-      },
-      each: {
-        overrides: {
-          'js/src/dom/polyfill.js': {
-            statements: 30,
-            lines: 30,
-            branches: 8,
-            functions: 30
-          }
-        }
       }
     }
   }