Remove Time Sync object's Associated Interface Objects attribute (29)

The Associated Interface Objects attribute (29) and Associated Interface Labels attribute (31) must be supported together.

Attribtue 29 is conditional. See CIP Volume 1:

This attribute is required if any of the following conditions are true:

1. A device supports more than one CIP port and it is not possible for the PTP and CIP port numbers to be the same or
2. More than one PTP port is associated with a single CIP port (e.g. PRP).

We support only one CIP port and only one PTP port.
Therefore, we don't have to support attribute 29 and 31.