message: [trivial] Remove misleading 'const'
  Returning by const value is only meaningful in a specific circumstance around
  user defined types. In this case, the const is not enforcing any restrictions
  on the call site, so is misleading.
diff: @@ -693,7 +693,7 @@ public:
  void RemoveUnbroadcastTx(const uint256& txid, const bool unchecked = false);
  /** Returns transactions in unbroadcast set */
  - const std::set<uint256> GetUnbroadcastTxs() const {
  + std::set<uint256> GetUnbroadcastTxs() const {
  LOCK(cs);
  return m_unbroadcast_txids;
  }
  