[FIX] web: overspecified test

Testing what's literally just a native feature seems odd, but in this
case it's also way over-specified: Firefox's error message for the
conversion of a symbol to a number is

    can't convert symbol to number

addons/web/static/tests/core/util_tests.js

@@ -231,7 +231,7 @@ QUnit.module('core', {}, function () {
         );
         assert.throws(
             () => sortBy([Symbol('b'), Symbol('a')]),
-            new TypeError(`Cannot convert a Symbol value to a number`)
+            TypeError
         );
         assert.throws(
             () => sortBy(ints, true),