a0efe529e4 Fix outdated comments referring to ::ChainActive() (Samuel Dobson)
Pull request description:
After #21866 there are a few outdated comments referring to `::ChainActive()`, which should instead refer to `ChainstateManager::ActiveChain()`.
ACKs for top commit:
jamesob:
ACK a0efe529e4
Tree-SHA512: 80da19c105ed29ac247e6df4c8e916c3bf3f37230b63f07302114eef9c115add673e9649f0bbe237295be0c6da7b1030b5b93e14daf6768f17ce5de7cf2c9ff2