Re-measure IterableMap

[sprunk]

Recent engines offer better tracing/profiling tools (Tracy) and Beherith claims that pairs(map) is faster than even the IterableMap.GetBarbarianData interface). Perhaps worth repeating whatever measurements had originally been made, or just measure existing use cases of iterable map, because if it's faster to just use pairs then most uses of iterable map can be thrown out (simplicity is king).

It does offer some nice features (constant-time count, random element, staggered iteration) so it shouldn't be completely removed though.