Multiple bug fixes / support for WP5.8 widget block editor

【Contents of the fix】
■Delete unnecessary items in the theme options.
■Fixed a bug where the header message was not displayed when viewed on a PC.
■【iPad】Fixed a bug that prevented tapping the second level or lower of the drawer menu in landscape mode.
■Support for the WordPress 5.8 widget block editor

【Modified files】
admin/inc/quicktag.php
admin/js/my_script.js
functions/head.php
languages/ja.mo
languages/ja.po
functions.php
style.css