Remove checkpoints

The headers presync logic should be enough to prevent memory DoS using
low-work headers. Therefore, we no longer have any use for checkpoints.

src/node/blockstorage.cpp

@@ -38,7 +38,6 @@
 
 #include <cstddef>
 #include <map>
-#include <ranges>
 #include <unordered_map>
 
 namespace kernel {
@@ -576,20 +575,6 @@ void BlockManager::ScanAndUnlinkAlreadyPrunedFiles()
     UnlinkPrunedFiles(block_files_to_prune);
 }
 
-const CBlockIndex* BlockManager::GetLastCheckpoint(const CCheckpointData& data)
-{
-    const MapCheckpoints& checkpoints = data.mapCheckpoints;
-
-    for (const MapCheckpoints::value_type& i : checkpoints | std::views::reverse) {
-        const uint256& hash = i.second;
-        const CBlockIndex* pindex = LookupBlockIndex(hash);
-        if (pindex) {
-            return pindex;
-        }
-    }
-    return nullptr;
-}
-
 bool BlockManager::IsBlockPruned(const CBlockIndex& block) const
 {
     AssertLockHeld(::cs_main);