Range<u64> implements ExactSizeIterator

[bluss]

What does (0..std::u64::MAX).size_hint() return on a 32-bit build? Range<u64> and Range<i64> cannot fulfill the requirements of the ExactSizeIterator trait, and the implementations must be removed.

[bluss]

I checked the code and it turns out the impl is conditional -- only on 64-bit platforms. So that's correct and for me it turned into a different question of whether that kind of platform dependence is good. I've started a discussion about that here.

[bluss]

Reopened, got some voices backing that this is a bug.

Soft solution would be to warn on using that particular impl of ExactSizeIterator for Range and i64, but I don't know if we can even do that.

Otherwise we can just remove the impls.