Remove payable fallback from Staking.sol

contracts/staking/contracts/src/Staking.sol

@@ -31,13 +31,6 @@ contract Staking is
     MixinStake,
     MixinExchangeFees
 {
-    // this contract can receive ETH
-    // solhint-disable no-empty-blocks
-    function ()
-        external
-        payable
-    {}
-
     /// @dev Initialize storage owned by this contract.
     ///      This function should not be called directly.
     ///      The StakingProxy contract will call it in `attachStakingContract()`.

contracts/staking/contracts/test/TestFinalizer.sol

@@ -63,6 +63,13 @@ contract TestFinalizer is
         _removeAuthorizedAddressAtIndex(msg.sender, 0);
     }
 
+    // this contract can receive ETH
+    // solhint-disable no-empty-blocks
+    function ()
+        external
+        payable
+    {}
+
     /// @dev Activate a pool in the current epoch.
     function addActivePool(
         bytes32 poolId,