test: turn on WPT tests on empty param pairs

This specific bug was fixed by #11234. This commit turns on the tests
accordingly.

PR-URL: #11369
Ref: #11234
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-whatwg-url-searchparams-stringifier.js

@@ -112,8 +112,8 @@ test(function() {
 
 test(function() {
     var params;
-    // params = new URLSearchParams('a=b&c=d&&e&&');
-    // assert_equals(params.toString(), 'a=b&c=d&e=');
+    params = new URLSearchParams('a=b&c=d&&e&&');
+    assert_equals(params.toString(), 'a=b&c=d&e=');
     // params = new URLSearchParams('a = b &a=b&c=d%20');
     // assert_equals(params.toString(), 'a+=+b+&a=b&c=d+');
     // The lone '=' _does_ survive the roundtrip.