Remove post type 'viewable' compatibility shim (#7496)

This was shipped with WordPress 4.9.6

lib/rest-api.php

@@ -365,39 +365,6 @@ function gutenberg_register_taxonomy_prepare_functions( $taxonomy ) {
 }
 add_filter( 'registered_taxonomy', 'gutenberg_register_taxonomy_prepare_functions' );
 
-/**
- * Includes the value for the 'viewable' attribute of a post type resource.
- *
- * @see https://core.trac.wordpress.org/ticket/43739
- *
- * @param object $post_type Post type response object.
- * @return boolean Whether or not the post type can be viewed.
- */
-function gutenberg_get_post_type_viewable( $post_type ) {
- return is_post_type_viewable( $post_type['slug'] );
-}
-
-/**
- * Adds the 'viewable' attribute to the REST API response of a post type.
- *
- * @see https://core.trac.wordpress.org/ticket/43739
- */
-function gutenberg_register_rest_api_post_type_viewable() {
- register_rest_field( 'type',
- 'viewable',
- array(
- 'get_callback' => 'gutenberg_get_post_type_viewable',
- 'schema' => array(
- 'description' => __( 'Whether or not the post type can be viewed', 'gutenberg' ),
- 'type' => 'boolean',
- 'context' => array( 'edit' ),
- 'readonly' => true,
- ),
- )
- );
-}
-add_action( 'rest_api_init', 'gutenberg_register_rest_api_post_type_viewable' );
-
 /**
  * Gets revisions details for the selected post.
  *