Deprecate nonscalar nextfastfft methods?

[ssfrr]

If a user has a dims tuple we currently have 3 different ways to call nextfastfft defined here:

• nextfastfft(dims)
• nextfastfft(dims...)
• nextfastfft.(dims)

In general this sort of automatic collection handling has been getting deprecated in favor of having the caller use broadcasting (option 3 above). I propose we deprecate the first 2.

It's possible that the multi-arg version (nextfastfft(x, y)) is useful, but I don't think that we as a general policy expand other single-arg functions in this way.