Some digging, but not a ton…right out of the valve box, you can run a tee of the line you are going to keep, and tie into the other singular “zone”. I’d recommend that you remove that decommissioned valve and cap off that PVC line after you are done…
If you want to make it really easy, and don’t care about having a valve there, but don’t see the purpose of a zone for just one plant, wire them both to the same terminal on the Rachio. Assuming you don’t have a master pump, and aren’t using the “water hammer” feature in Rachio, then Rachio can power up to 3 zones off one terminal.