Authwit code reference fix

[catmcgee]

mike: I was just brushing up on authwits, and this code snippet in this section seems to have been modified so that it no-longer demonstrates any authwit functionality, meaning the text below the code snippet is out of date. Perhaps the name of the docs:start: wasn't descriptive enough to hint to the engineer that their code changes might break commentary on authwits. https://docs.aztec.network/guides/smart_contracts/writing_contracts/authwit#checking-if-the-current-call-is-authenticated

[critesjosh]

closed by AztecProtocol/aztec-packages#7640