Handle an empty service_id list in cloudi_service_api:services_remove/2

`cloudi_service_api:services_remove/2` won't match against:

`cloudi_service_api:services_remove([],Timeout)`

If there's possibility that the service list you pass is empty, you must use handle it with awkward `case`:

<pre>
Result = case ServiceIdList of 
    [ ] ->
        ok;
    [ _ : _ ] ->
        cloudi_service_api:services_remove(ServiceIdList,Timeout)
end.
</pre>

It seems easier to handle the empty list case in `cloudi_service_api`.