conflict fixes

contracts/mocks/SafeERC20Helper.sol

@@ -36,10 +36,6 @@ contract ERC20FailingMock is IERC20 {
   function allowance(address, address) public view returns (uint256) {
     return 0;
   }
-  
-  function setAllowance(uint256 value) public {
-    _allowance = value;
-  }
 }
 
 contract ERC20SucceedingMock is IERC20 {
@@ -153,17 +149,4 @@ contract SafeERC20Helper {
   function doSucceedingApprove() public {
     _succeeding.safeApprove(address(0), 0);
   }
-
-  function doFailingApproveByValue() public {
-    _succeeding.setAllowance(10);
-    _succeeding.safeApprove(address(0), 10);
-  }
-
-  function doSucceedingIncreaseAllowance() public {
-    _succeeding.safeIncreaseAllowance(address(0), 0);
-  }
-
-  function doSucceedingDecreaseAllowance() public {
-    _succeeding.safeDecreaseAllowance(address(0), 0);
-  }
 }

contracts/token/ERC20/IERC20.sol

@@ -17,15 +17,6 @@ interface IERC20 {
 
     function transferFrom(address from, address to, uint256 value) external returns (bool);
 
-  function increaseAllowance(address spender, uint256 addedValue) 
-    external returns (bool);
-
-  function decreaseAllowance(address spender, uint256 subtractedValue) 
-    external returns (bool);
-
-  function setAllowance(uint256 value) 
-    external returns (bool);
-
   event Transfer(
     address indexed from,
     address indexed to,

test/token/ERC20/SafeERC20.test.js

@@ -98,16 +98,4 @@ contract('SafeERC20', function () {
       });
     });
   });
-
-  it('should throw while approving with non-zero existing allowance', async function () {
-    await shouldFail.reverting(this.helper.doFailingApproveByValue());
-  });
-
-  it('should not throw on succeeding increaseAllowance', async function () {
-    await this.helper.doSucceedingIncreaseAllowance();
-  });
-
-  it('should not throw on succeeding decreaseAllowance', async function () {
-    await this.helper.doSucceedingDecreaseAllowance();
-  });
 });