Fixed a bug regarding the “main photo” of posts

【Details of the fix】
■Fixed a bug where the main photo of a post could not be deleted completely.
■Fixed a duplication in the processing of the “Main Image”.

The following files have been modified for this update.
【Fixed files】
admin/js/meta_image_delete.js
functions/membership/blog.php
functions/membership/main_image.php
functions/membership/photo.php
functions/membership/user_profile.php
style.css