@TheDeadMedic was right, in my second code snippet, admin_init
should be admin_menu
. That solved my problem, thanks a lot to all of you!
Corrected code:
//remove from menu
function remove_posts_menu() {
remove_menu_page('edit.php');
remove_menu_page('edit.php?post_type=page');
remove_menu_page('edit-comments.php' );
}
add_action('admin_menu', 'remove_posts_menu');