Remove all traces of the classic editor in Gutenberg

disable-classic-editor.php

<?php

/**
 * Removes the classic editor actions links.
 */
add_action( 'admin_init', function() {
	// For hierarchical post types.
	add_filter( 'page_row_actions', 'gutenberg_remove_classic_editor_links', 10, 2 );
	// For non-hierarchical post types.
	add_filter( 'post_row_actions', 'gutenberg_remove_classic_editor_links', 10, 2 );
} );

/**
 * Removes additional link in the post/page screens to edit any post/page in
 * the Classic editor.
 *
 * @param  array   $actions Post actions.
 * @param  WP_Post $post    Edited post.
 *
 * @return array          Updated post actions.
 */
function gutenberg_remove_classic_editor_links( $actions, $post ) {
	unset( $actions['classic'] );
	return $actions;
}

/**
 * Hide Classic Editor dropdown from create post.
 */
add_action( 'admin_print_scripts-edit.php', function() {
	?><style type="text/css">.split-page-title-action .expander{display:none;}</style><?php
}, 11 );