Remove complex rendering.

There wasn't a complex option type in 2.x, so there isn't much reason to
add it.

src/View/Input/MultiCheckbox.php

@@ -41,6 +41,7 @@ class MultiCheckbox {
  *   checked.
  * - `disabled` Either a boolean or an array of checkboxes to disable.
  * - `escape` Set to false to disable HTML escaping.
+ * - `options` An associative array of value=>labels to generate options for.
  *
  * @param array $data
  * @return string

tests/TestCase/View/Input/MultiCheckboxTest.php

@@ -107,15 +107,6 @@ class MultiCheckboxTest extends TestCase {
 	}
 
 /**
- * Test render complex options.
- *
- * @return void
- */
-	public function testRenderComplex() {
-		$this->markTestIncomplete();
-	}
-
-/**
  * Test render selected checkboxes.
  *
  * @return void