We need to rethink remove in std.container

[%u]

You know, I'm actually now questioning whether STL did the right thing
with requiring iterators for the erase() method. It actually seems
quite pointless -- there's no reason why integer indices wouldn't
work. I don't think we really need to follow suit with STL here... is
there some situation with erase() that I'm missing that can't be
covered with plain integer (or rather, size_t) indices, and that
requires ranges?