The getActiveChainLocator method name was misleading, and its functionality
duplicated `Chain::findBlock`. This commit removes the method and replaces
all its usages with direct `Chain::findBlock` calls.
Additionally, the comment of getActiveChainLocator has been outdated since
commit ed47094 from #25717.
Finally, in CWallet::ScanForWalletTransactions, the findBlock calls are now
unified into a single call at the start of the function.
Co-authored-by: Ryan Ofsky <ryan@ofsky.org>
Co-authored-by: Matias Furszyfer <mfurszy@protonmail.com>
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