How can I remove this floor transition, and what should it be replaced with once I lay LVP?
Why remove it?  It's matched perfectly to the floor outside the room, and you have vinyl now so just slice the vinyl carefully where it meets the wood now, and if the new floor is a bit thicker it'll level up perfectly and look great.    If the new floor is higher than the wood floor add a narrow brass threshhold to protect its edge.