Force disabling of the expanded editor option in WordPress

gistfile1.txt

add_action( 'init', 'gowp_disable_editor_expand_setting' );
function gowp_disable_editor_expand_setting() {
	global $_updated_user_settings;
	$_updated_user_settings['editor_expand'] = 'off';
}

add_action( 'admin_footer', 'gowp_disable_editor_expand_field' );
function gowp_disable_editor_expand_field() {
	$screen = get_current_screen();
	if ( 'post' == $screen->base ) : ?>
		<script type="text/javascript">
			jQuery( document ).ready( function() {
				jQuery( '#editor-expand-toggle' ).prop( 'disabled', true );
			} );
		</script>
	<?php endif;
}

@shackep also, just found this in core trac, which is cleaner.

add_action( 'admin_init', 'my_deregister_editor_expand' );
function my_deregister_editor_expand() {
    wp_deregister_script('editor-expand');
}

add_filter( 'tiny_mce_before_init', 'my_unset_autoresize_on' );
function my_unset_autoresize_on( $init ) {
    unset( $init['wp_autoresize_on'] );
    return $init;
}