chore: remove function in interface + small modif NATSPECs

src/interfaces/IERC20.sol

@@ -3,6 +3,4 @@ pragma solidity >=0.5.0;
 
 /// @dev Empty because we only call functions in assembly. It prevents calling
 /// transfer (transferFrom) instead of safeTransfer (safeTransferFrom).
-interface IERC20 {
-    function balanceOf(address owner) external view returns (uint256);
-}
+interface IERC20 {}

src/interfaces/IFlashBorrower.sol

@@ -2,12 +2,10 @@
 pragma solidity >=0.5.0;
 
 interface IFlashBorrower {
-    /**
-     * @dev Receives a flash loan.
-     * @param initiator The initiator of the loan.
-     * @param token The token lent.
-     * @param amount The amount of tokens lent.
-     * @param data Arbitrary data structure, intended to contain user-defined parameters.
-     */
+    /// @dev Receives a flash loan.
+    /// @param initiator The initiator of the loan.
+    /// @param token The token lent.
+    /// @param amount The amount of tokens lent.
+    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
     function onFlashLoan(address initiator, address token, uint256 amount, bytes calldata data) external;
 }

src/interfaces/IFlashLender.sol

@@ -4,12 +4,10 @@ pragma solidity >=0.5.0;
 import {IFlashBorrower} from "src/interfaces/IFlashBorrower.sol";
 
 interface IFlashLender {
-    /**
-     * @dev Initiate a flash loan.
-     * @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
-     * @param token The token lent.
-     * @param amount The amount of tokens lent.
-     * @param data Arbitrary data structure, intended to contain user-defined parameters.
-     */
+    /// @dev Initiate a flash loan.
+    /// @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
+    /// @param token The token lent.
+    /// @param amount The amount of tokens lent.
+    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
     function flashLoan(IFlashBorrower receiver, address token, uint256 amount, bytes calldata data) external;
 }