您必须在notifyDataSetChanged();

 holder.btnDeleteBookmark.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {

        String  id = cursor.getString(0);

        mDBHelper.deleteBookmark(id);

        //here
       notifyItemRemoved(holder.getAdapterPosition());
       notifyDataSetChanged();

    }
});