move-only: Move CBlockIndexWorkComparator to blockstorage

...it's declared in blockstorage.h

src/node/blockstorage.cpp

@@ -28,6 +28,25 @@ bool fHavePruned = false;
 bool fPruneMode = false;
 uint64_t nPruneTarget = 0;
 
+bool CBlockIndexWorkComparator::operator()(const CBlockIndex* pa, const CBlockIndex* pb) const
+{
+    // First sort by most total work, ...
+    if (pa->nChainWork > pb->nChainWork) return false;
+    if (pa->nChainWork < pb->nChainWork) return true;
+
+    // ... then by earliest time received, ...
+    if (pa->nSequenceId < pb->nSequenceId) return false;
+    if (pa->nSequenceId > pb->nSequenceId) return true;
+
+    // Use pointer address as tie breaker (should only happen with blocks
+    // loaded from disk, as those all have id 0).
+    if (pa < pb) return false;
+    if (pa > pb) return true;
+
+    // Identical blocks.
+    return false;
+}
+
 static FILE* OpenUndoFile(const FlatFilePos& pos, bool fReadOnly = false);
 static FlatFileSeq BlockFileSeq();
 static FlatFileSeq UndoFileSeq();