Remove expensive, pointless typeachecking in custom fields

Summary:
Ref T11404. On my system, this improves performance by 10-15% for `differential.revision.search`.

`PhutilTypeSpec` provides high quality typechecking and is great for user-facing things that need good error messages.

However, it's also a bit slow, and pointless here (the API is internal and it only has one possible option).

I think I added this after writing `checkMap` just because I wanted to use it more often. My desire is sated after finding many reasonable ways to use it to give users high-quality error messages about things like configuration files.

Test Plan: Profiled `differential.revision.search` before and after change, saw wall time drop from ~220ms to ~195ms.

Reviewers: yelirekim, chad

Reviewed By: chad

Maniphest Tasks: T11404

Differential Revision: https://secure.phabricator.com/D16354

src/infrastructure/customfield/field/PhabricatorCustomField.php

@@ -112,12 +112,6 @@ abstract class PhabricatorCustomField extends Phobject {
     $object,
     array $options = array()) {
 
-    PhutilTypeSpec::checkMap(
-      $options,
-      array(
-        'withDisabled' => 'optional bool',
-      ));
-
     $field_objects = id(new PhutilSymbolLoader())
       ->setAncestorClass($base_class)
       ->loadObjects();