code: public boolean deletePermissionForUser(String user, List<String> permission) {
          return deletePermissionForUser(user, permission.toArray(new String[0]));
      }
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.