But I don't see that being likely. OC is one of the few disney based worlds from KH1 that can show age differences along with Atlantica so i do not think OC has been cut.
It doesn't matter, Olympus isn't necessarily important, even if age differences can be used.
Let's say Nomura put in a certain amount of worlds, but couldn't fit in Atlantica, which is much more important. He might have to remove a world, and with Olympus being in every single game, decided to remove that one because he wants everything to be fresh in Birth by Sleep.
It really depends how much they can fit on the UMD though.