message: chain: Remove UB CChain comparison
  It was unused, and had UB
diff: @@ -505,12 +505,6 @@ public:
  return vChain[nHeight];
  }
  - /** Compare two chains efficiently. */
  - friend bool operator==(const CChain &a, const CChain &b) {
  - return a.vChain.size() == b.vChain.size() &&
  - a.vChain[a.vChain.size() - 1] == b.vChain[b.vChain.size() - 1];
  - }
  -
  /** Efficiently check whether a block is present in this chain. */
  bool Contains(const CBlockIndex *pindex) const {
  return (*this)[pindex->nHeight] == pindex;
  