Remove balance api leftovers in db and txlog parsers

[ray-roestenburg-da]

After #3503 we should also be able to cleanup the dbs and txlog parsers further, perhaps in multiple steps:

1. make the columns here and in the scan txlog only required for the balances nullable
2. stop writing those fields
3. (eventually nuke those columns)

at least 1 and 2 as it meaningfully simplifies the code.