Incorrect comment on EB announcement field

This comment is wrong

https://github.com/IntersectMBO/cardano-ledger/blob/ae2c8912b204d11e102faeb617b6faa6a8c9f934/libs/cardano-protocol/src/Cardano/Protocol/Leios/BlockHeader.hs#L88-L89

That field is not the size of the closure, it's the size of the body itself --- aka it's the size of the sequence of pairs of tx hashes and tx sizes (I don't remember the new name for that... EndorserBlock? Refs? 🤷 ), it's not the sum of that sequence of tx sizes.

`git grep -w -e` says that definition is the only occurrence of the field name. So hopefully no implementation logic anywhere is already trusting that incorrect comment.