Remove unneeded (now) ignore from the validator.

Gruntfile.js

@@ -223,7 +223,6 @@ module.exports = function (grunt) {
         reset: true,
         relaxerror: [
           'Attribute ontouchstart not allowed on element body at this point.',
-          'Bad value X-UA-Compatible for attribute http-equiv on element meta.',
           'Consider using the h1 element as a top-level heading only \\(all h1 elements are treated as top-level headings by many screen readers and other tools\\)\\.'
         ]
       },