remove R.indexOf.from and R.lastIndexOf.from

I imagine these functions were added because [`Array.prototype.indexOf`][1] takes an optional second argument. I haven't used either function, and even when they're useful they're not necessary (though they avoid array cloning).

If we decide to *keep* these functions, let's make them top-level functions.


[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/indexOf