3.0 merges simplified

For consistency across 3.0 classes. It's also 5-7x faster.

The (dead) removed line in src/View/Helper.php probably needs some follow up @AD7six
It was introduced in https://github.com/cakephp/cakephp/commit/12b281ac7bc678454c0e9d2e1f3a0c2055d02792#diff-73cae20de0f595ea9d7dcbe7610774f7R180

There might be a missing test case for `'enabled' => false/true`
Should change to new array syntax too.