Removed unnecessary Secondary inheritance from RefundEscrow. (#1381)

Author: nventuro

contracts/payment/RefundEscrow.sol

@@ -1,15 +1,14 @@
 pragma solidity ^0.4.24;
 
 import "./ConditionalEscrow.sol";
-import "../ownership/Secondary.sol";
 
 /**
  * @title RefundEscrow
  * @dev Escrow that holds funds for a beneficiary, deposited from multiple parties.
  * The primary account may close the deposit period, and allow for either withdrawal
  * by the beneficiary, or refunds to the depositors.
  */
-contract RefundEscrow is Secondary, ConditionalEscrow {
+contract RefundEscrow is ConditionalEscrow {
   enum State { Active, Refunding, Closed }
 
   event Closed();