REST API: Only include the controller's own taxonomy in it's schema.

Previously, all taxonomies were incorrectly exposed as possible values.

Props johnbillion.
Fixes #51940.

Built from https://develop.svn.wordpress.org/trunk@49922


git-svn-id: http://core.svn.wordpress.org/trunk@49621 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/endpoints/class-wp-rest-terms-controller.php

@@ -965,7 +965,7 @@ class WP_REST_Terms_Controller extends WP_REST_Controller {
 				'taxonomy'    => array(
 					'description' => __( 'Type attribution for the term.' ),
 					'type'        => 'string',
-					'enum'        => array_keys( get_taxonomies() ),
+					'enum'        => array( $this->taxonomy ),
 					'context'     => array( 'view', 'embed', 'edit' ),
 					'readonly'    => true,
 				),