SPARK-2146.  Fix takeOrdered doc

Removes Python syntax in Scaladoc, corrects result in Scaladoc, and removes irrelevant cache() call in Python doc.
Extremely minor - but it would be better to use `Seq` instead of `Array` in these examples. Otherwise people might think they need to pass an `Array` to `parallelize` whereas in fact it accepts more widely than that. I looked and we actually use `Array` in one other place in the current codebase, we should separately probably change that.