saving throws warning

[behinger]

@jschepers reported:
StatsModels.FunctionTerm{typeof(Unfold.spl),Main.#14#22,(:dg_log_prob_next,)}; reconstructing"

when loading a model with deconvolution + splines.

I thought removing the spline anonymous function should have been enough (as in Unfold 0.5.0) - but there is still one in the BasisFunctions -> we have to check whether removing that one removes the wanring as well