contract_code_hash in history_operations is retrieved incorrectly

[chowbao]

https://stellarfoundation.slack.com/archives/C073MNCNVQQ/p1775514429420589?thread_ts=1775506491.001509&cid=C073MNCNVQQ

Currently we use the first contract_code_hash in the read_only footprint and have assumed that this hash is the contract_code for the parent contract_id (the invoking contract). This is incorrect

Determine if contract_code for the parent contract_id is the last contract_code_hash entry in the read_only footprint. If not determine how to find out the parent contract_id's contract_code_hash

[amishas157]

Drop the contract_code_hash altogether based on discussion with team.
Make the value null, so as to not change schema for Dune