Remove unused wp-nux CSS dependency.

See
* WordPress/wordpress-develop@8a6afdd
* https://core.trac.wordpress.org/ticket/57827

lib/client-assets.php

@@ -269,7 +269,7 @@ function gutenberg_register_packages_styles( $styles ) {
 		$styles,
 		'wp-editor',
 		gutenberg_url( 'build/editor/style.css' ),
-		array( 'wp-components', 'wp-block-editor', 'wp-nux', 'wp-reusable-blocks' ),
+		array( 'wp-components', 'wp-block-editor', 'wp-reusable-blocks' ),
 		$version
 	);
 	$styles->add_data( 'wp-editor', 'rtl', 'replace' );
@@ -278,7 +278,7 @@ function gutenberg_register_packages_styles( $styles ) {
 		$styles,
 		'wp-edit-post',
 		gutenberg_url( 'build/edit-post/style.css' ),
-		array( 'wp-components', 'wp-block-editor', 'wp-editor', 'wp-edit-blocks', 'wp-block-library', 'wp-commands', 'wp-nux' ),
+		array( 'wp-components', 'wp-block-editor', 'wp-editor', 'wp-edit-blocks', 'wp-block-library', 'wp-commands' ),
 		$version
 	);
 	$styles->add_data( 'wp-edit-post', 'rtl', 'replace' );