removeAuthority(parentGroup, authority) removes an authority
      from a group.
    Parameters
- parentGroup
- The node representing the group to remove the user or group from.
- authority
- A node representing the user or group to remove.
Example
The following code will remove the user abeecher from the test group.
var group = people.getGroup("GROUP_TEST");
if(group){
    user = people.getPerson("abeecher");
    try{
        people.removeAuthority(group, user);
    }
    catch (ex){
        model.message = "ABORT: Exception occurred: "+ex;
        return;
    }
}
      If a probem occurs, for example the user cannot be found, an exception message will be generated such as the following:
        ABORT: Exception occurred: JavaException: java.lang.IllegalArgumentException: Authority is a mandatory parameter
      
    