REST API: Revert widget endpoints

Reverts [50993] as it has missing props.

Reverts [50993].
See #41683.


git-svn-id: https://develop.svn.wordpress.org/trunk@50994 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/widgets/class-wp-widget-rss.php

@@ -25,8 +25,6 @@ class WP_Widget_RSS extends WP_Widget {
 		$widget_ops  = array(
 			'description'                 => __( 'Entries from any RSS or Atom feed.' ),
 			'customize_selective_refresh' => true,
-			'show_instance_in_rest'       => true,
-
 		);
 		$control_ops = array(
 			'width'  => 400,