Take a look at https://github.com/code-423n4/2024-03-zksync/blob/4f0ba34f34a864c354c7e8c47643ed8f4a250e13/code/system-contracts/contracts/libraries/TransactionHelper.sol#L89-L97
This function is used to know whether the address passed is th Ether address, and also returns true if the address passed is 0x0 (for conveniency) as stated here, issue with this is tht using this search command: https://github.com/search?q=repo%3Acode-423n4%2F2024-03-zksync+isEthToken&type=code we can see that this function is not used anywhere.
Remove redundant code as they most of the time hint flawed implementation.
Remove the isEthToken() function since its not being used anywhere.
