Clean up the script that is used to migrate legacy withdrawals.
This script is very important for testing the legacy withdrawal
migration.

A bug was introduced with https://github.com/ethereum-optimism/optimism/pull/4911
which was a sherlock audit fix. This was a bug because the change
resulted in the withdrawal hashes changing, meaning that the storage
slots computed client side also changed. This resulted in breaking the
script. This commit reverts this change. The changes landing in
https://github.com/ethereum-optimism/optimism/pull/5470 will cause the
buffer in the gas limit for the  migrated withdrawals to be too small,
so we can reintroduce this code behind a switch with the network.
Its not ideal that the migration code isn't going to match 1:1
with goerli but thats ok because we will be able to thoroughly
test it.