Avoid running hasMetaBoxes on each subscribe (#15041)

packages/edit-post/src/store/effects.js

@@ -45,11 +45,16 @@ const effects = {
 
 		let wasSavingPost = select( 'core/editor' ).isSavingPost();
 		let wasAutosavingPost = select( 'core/editor' ).isAutosavingPost();
+
+		// Meta boxes are initialized once at page load. It is not necessary to
+		// account for updates on each state change.
+		//
+		// See: https://github.com/WordPress/WordPress/blob/5.1.1/wp-admin/includes/post.php#L2307-L2309
+		const hasActiveMetaBoxes = select( 'core/edit-post' ).hasMetaBoxes();
 		// Save metaboxes when performing a full save on the post.
 		subscribe( () => {
 			const isSavingPost = select( 'core/editor' ).isSavingPost();
 			const isAutosavingPost = select( 'core/editor' ).isAutosavingPost();
-			const hasActiveMetaBoxes = select( 'core/edit-post' ).hasMetaBoxes();
 
 			// Save metaboxes on save completion, except for autosaves that are not a post preview.
 			const shouldTriggerMetaboxesSave = (