Upgrade/Install: Add missing file to the $_old_files array.

Follow-up to [60490], [61338].

Props WFMattR, sajib1223, davidbaumwald, mukesh27, SergeyBiryukov.
Fixes #64336.

git-svn-id: https://develop.svn.wordpress.org/trunk@61351 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/update-core.php

@@ -847,6 +847,7 @@
 	'wp-includes/blocks/post-author/editor-rtl.css',
 	'wp-includes/blocks/post-author/editor-rtl.min.css',
 	'wp-includes/SimplePie/src/Decode',
+	'wp-includes/SimplePie/src/Core.php',
 );
 
 /**