We have just finished completely reworking the calendar system. It will be in the next update.
In the meantime, no you can't just delete whichever one you want. One is attached to APDL and the other is just a duplicate that won't be updated (unless you're using two devices).
The only way to determine which entry will be updated by APDL is to make a change to one of the times and see which one changes. The other one can be deleted.
Alternatively, you could delete both entries and let APDL just create a new one when you update it with actual times. You could do this by manually deleting the calendar entries from your calendar or by using the delete all future events option in the APDL calendar settings.
Of course this would remove your future legs from the calendar. To re add them you'd have to go to every leg, make a small edit, and save.
All of that is not ideal I know, but it's just in the meantime until the next update is released by apple.