Remove empty foreign key test.

Foreign keys are not needed for the very first step of
re-factoring/building this feature. I'll add them back later on.

lib/Cake/Database/Schema/Table.php

@@ -172,6 +172,7 @@ public function column($name) {
  * - `type` The type of index being added.
  * - `columns` The columns in the index.
  *
+ * @TODO implement foreign keys.
  * @param string $name The name of the index.
  * @param array $attrs The attributes for the index.
  * @return Table $this

lib/Cake/Test/TestCase/Database/Schema/TableTest.php

@@ -131,12 +131,4 @@ public function testAddIndexTypes() {
 		]);
 	}
 
-/**
- * Test adding foreign keys.
- *
- * @return void
- */
-	public function testAddIndexForeign() {
-	}
-
 }