The checkpoints were formerly copied from the full node, so based
on possible fork-events.
That seems less useful nowadays and since we want to be able to
allow starting a blockchain instance from any checkpoint it makes
sense to spread them out more evenly.
Based on the concept that the BCH chain generates around 50K blocks
a year, we simply use that interval.
This removes various very old ones meaning that the total count is
roughly equal.
tomFlowee
9008b4a312