0x715018a6?0x715018a6 is the function selector for renounceOwnership(). Permanently gives up control of the contract.
When a transaction's data begins with 0x715018a6, it is calling renounceOwnership. The selector is the first four bytes of the keccak-256 hash of the signature renounceOwnership(), which is how wallets and explorers work out which function a payload is for.