remove custom post type permalink

Well, there is another way. And better, I guess.

You should look at register_post_type parameters. You should probably set them like this:

'public' => false,  // it's not public, it shouldn't have it's own permalink, and so on
'publicly_queryable' => true,  // you should be able to query it
'show_ui' => true,  // you should be able to edit it in wp-admin
'exclude_from_search' => true,  // you should exclude it from search results
'show_in_nav_menus' => false,  // you shouldn't be able to add it to menus
'has_archive' => false,  // it shouldn't have archive page
'rewrite' => false,  // it shouldn't have rewrite rules

If post type is not public, then you won’t see this part of editor.