To be consistent with [python-opentimestamps](https://github.com/opentimestamps/python-opentimestamps/blob/master/opentimestamps/core/timestamp.py#L75), when checking [if two timestamps are equal](https://github.com/opentimestamps/java-opentimestamps/blob/master/src/main/java/com/eternitywall/ots/Timestamp.java#L512), attestations should not be checked.