Avoid extra uses of Iterator.ts

[mjbvz]

• Removes Iterator.equals as this method is completely unused except in a test
• Replace Iterator.collect with Array.from
• Use asArray instead of Iterable.single in a few cases
• Remove Iterable.forEach and replace single caller with for/of lopp
• If passing an array to one of the other Iterable methods, we don't need to call Iterable.from on it first
• When we create an iterable from an array and then convert that iterable back to an array right away, we should just operate on the array (this lets us remove the one caller of Iterable.concatNested)

[jrieken]

Use asArray instead of Iterable.single in a few cases

Is that actually better? The asArray-util always creates a new array which can be avoided with single (and was the reasons for its existence). Maybe a better pattern for Array.isArray(prefix) ? prefix : Iterable.single(prefix) is needed, something like Iterator.wrap(n) where n is iterable or a single item