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 `RoleService::removePolicy()` and and adds InvalidArgumentException when policy does not belong to the given role. New method is implemented: `RoleService::deletePolicy( Policy $policy )`.

`UserHandler::removePolicy( $roleId, $policyId )` is changed to `UserHandler::deletePolicy( $policyId )`.