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);

src/node/blockstorage.h

@@ -357,9 +357,6 @@ public:
     /** Calculate the amount of disk space the block & undo files currently use */
     uint64_t CalculateCurrentUsage();
 
-    //! Returns last CBlockIndex* that is a checkpoint
-    const CBlockIndex* GetLastCheckpoint(const CCheckpointData& data) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
-
     //! Check if all blocks in the [upper_block, lower_block] range have data available.
     //! The caller is responsible for ensuring that lower_block is an ancestor of upper_block
     //! (part of the same chain).

src/node/chainstatemanager_args.cpp

@@ -29,8 +29,6 @@ util::Result<void> ApplyArgsManOptions(const ArgsManager& args, ChainstateManage
         opts.check_block_index = args.GetArg("-checkblockindex")->empty() ? 1 : *value;
     }
 
-    if (auto value{args.GetBoolArg("-checkpoints")}) opts.checkpoints_enabled = *value;
-
     if (auto value{args.GetArg("-minimumchainwork")}) {
         if (auto min_work{uint256::FromUserHex(*value)}) {
             opts.minimum_chain_work = UintToArith256(*min_work);