code: public boolean deletePermissionForUser(String user, String... permission) {
          List<String> params = new ArrayList<>();
  
          params.add(user);
          Collections.addAll(params, permission);
  
          return removePolicy(params);
      }
docs: deletePermissionForUser deletes a permission for a user or role.
  Returns false if the user or role does not have the permission (aka not affected).
  
  @param user the user.
  @param permission the permission, usually be (obj, act). It is actually the rule without the subject.
  @return succeeds or not.