Fix EZP-21045: RemovePolicy method does remove the passed policy regarding the role it is in

This PR resolves issue https://jira.ez.no/browse/EZP-21045

In the method `RoleService::removePolicy( Role $role, Policy $policy )` first parameter is actually not needed, as Policy can be associated to exactly one Role.

This deprecates $role parameter as far as that can be done, given it is a first parameter.
Method signature should be changed with version 6.