Consider removing direct dependency on DataFrames

[Sbozzolo]

DataFrames is an heavy dependency. Currently, it is used only in the neural snow model (which we can move to an extension) and in the PFTs (https://github.com/CliMA/ClimaLand.jl/blob/main/src/standalone/Vegetation/pfts.jl)

It would be great if we could avoid using DataFrames in pfts.jl as that would allow us to remove the dependency