unify R.clone, R.cloneObj, and R.cloneDeep

Currently we have three clone functions which do slightly different things. `R.cloneDeep` is strictly more capable than `R.clone`, so `R.clone` can be removed. The only reason to keep `R.cloneObj` is to support shallow cloning. In my experience this is rarely desirable.

This pull request:

1.  removes `R.clone` and accompanying tests;
2.  removes `R.cloneObj` and accompanying tests; and
3.  renames `R.cloneDeep` `R.clone`.

Do you agree one clone function is sufficient?