Change DataStructures dependency with OrderedCollections

[oameye]

Hey hey, I noticed that we use DataStructures.jl, the parent of OrderedCollections.jl. However, I think, we only use the OrderedDict type defined in OrderedCollections.jl. Hence, we only need the OrderedCollections.jl dependency. Although, opting for OrderedCollections.jl would not reduce are loading time by much. I think it is just cleaner to only load what you use. This is also suggested in the SCIML style guide.