remove R.reduce and R.reduceRight

Many found this [parable][1] persuasive. There's support for removing the remaining :alien:s.

I set to work on a patch to *remove* `R.foldl` and `R.foldr`, but as I worked my way through the various files I became convinced that it's `R.reduce` and `R.reduceRight` that must go. Here are my reasons:

  - `foldl` and `foldr` are well liked. Several people have these in their shortlists of aliases to keep.

  - `foldl` and `foldr` are more consistent with our ad hoc naming scheme. We have `lPartial` and `rPartial`, for example, rather than `partial` and `partialRight`.

  - We have a function named `unfoldr`. It's inconsistent to have `reduceRight` and `unfoldr`, and `unreduceRight` doesn't exactly roll off the tongue.

I'd love to merge this change and rebase #618 on top of it. The intersection of two ugly things (:alien:s and `.idx` functions) is particularly confusing when every function lives in its own file.


[1]: https://github.com/ramda/ramda/pull/574#issuecomment-64124850

#620