Remove binary versions of processes?

[m-mohr]

We seem to conclude that having a process reduce_spatial(raster-cube, process, context) -> raster-cube is the way to go. [...]

One thing that came to mind is that for aggregate_spatial and reduce_dimension we have the binary variants (e.g. reduce_dimension_binary). We'd need a binary variant also for reduce_spatial, but on the other hand, I'm wondering whether we should remove these binary variants for now? There's no implementation yet and I've also not heard that anyone is actually planning to implement one of them.

Originally posted by @m-mohr in #226 (comment)

They were experimental before, so we can easily remove them without breaking change.