Refactor coordinator to use new ITransactions interface

contracts/coordinator/contracts/src/MixinCoordinatorCore.sol

@@ -55,11 +55,6 @@ contract MixinCoordinatorCore is
         );
 
         // Execute the transaction
-        EXCHANGE.executeTransaction(
+        EXCHANGE.executeTransaction(transaction, transactionSignature);
-            transaction.salt,
-            transaction.signerAddress,
-            transaction.data,
-            transactionSignature
-        );
     }
 }

contracts/coordinator/contracts/src/interfaces/ITransactions.sol

@@ -1,35 +0,0 @@
-/*
-
-  Copyright 2018 ZeroEx Intl.
-
-  Licensed under the Apache License, Version 2.0 (the "License");
-  you may not use this file except in compliance with the License.
-  You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-  Unless required by applicable law or agreed to in writing, software
-  distributed under the License is distributed on an "AS IS" BASIS,
-  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  See the License for the specific language governing permissions and
-  limitations under the License.
-
-*/
-pragma solidity ^0.5.5;
-
-
-contract ITransactions {
-
-    /// @dev Executes an exchange method call in the context of signer.
-    /// @param salt Arbitrary number to ensure uniqueness of transaction hash.
-    /// @param signerAddress Address of transaction signer.
-    /// @param data AbiV2 encoded calldata.
-    /// @param signature Proof of signer transaction by signer.
-    function executeTransaction(
-        uint256 salt,
-        address signerAddress,
-        bytes calldata data,
-        bytes calldata signature
-    )
-        external;
-}

contracts/coordinator/contracts/src/libs/LibConstants.sol

@@ -18,7 +18,7 @@
 
 pragma solidity ^0.5.5;
 
-import "../interfaces/ITransactions.sol";
+import "@0x/contracts-exchange/contracts/src/interfaces/ITransactions.sol";
 
 
 // solhint-disable var-name-mixedcase