chore: Remove erc20 dependency (SC-4209) (#6)

* chore: use IERC20Like instead of IERC20

* dapp uninstall erc20

.gitmodules

@@ -1,6 +1,3 @@
-[submodule "lib/erc20"]
-	path = lib/erc20
-	url = https://github.com/maple-labs/erc20.git
 [submodule "lib/ds-test"]
 	path = lib/ds-test
 	url = https://github.com/dapphub/ds-test.git

src/ERC20Helper.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 pragma solidity ^0.8.7;
 
-import { IERC20 } from "../lib/erc20/src/interfaces/IERC20.sol";
+import { IERC20Like } from "./interfaces/IERC20Like.sol";
 
 /**
  * @title Small Library to standardize erc20 token interactions. 
@@ -15,15 +15,15 @@ library ERC20Helper {
     /**************************/
 
     function transfer(address token, address to, uint256 amount) internal returns (bool) {
-        return _call(token, abi.encodeWithSelector(IERC20.transfer.selector, to, amount));
+        return _call(token, abi.encodeWithSelector(IERC20Like.transfer.selector, to, amount));
     }
 
     function transferFrom(address token, address from, address to, uint256 amount) internal returns (bool) {
-        return _call(token, abi.encodeWithSelector(IERC20.transferFrom.selector, from, to, amount));
+        return _call(token, abi.encodeWithSelector(IERC20Like.transferFrom.selector, from, to, amount));
     }
 
     function approve(address token, address spender, uint256 amount) internal returns (bool) {
-        return _call(token, abi.encodeWithSelector(IERC20.approve.selector, spender, amount));
+        return _call(token, abi.encodeWithSelector(IERC20Like.approve.selector, spender, amount));
     }
 
     function _call(address token, bytes memory data) private returns (bool success) {

src/interfaces/IERC20Like.sol

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+pragma solidity ^0.8.7;
+
+/// @title Interface of the ERC20 standard as needed by ERC20Helper
+interface IERC20Like {
+
+    function approve(address spender, uint256 amount) external returns (bool);
+
+    function transfer(address recipient, uint256 amount) external returns (bool);
+
+    function transferFrom(address owner, address recipient, uint256 amount) external returns (bool);
+
+}