[1/2][FA migration] Drop generated fields and add KS for unified

[bowenyang007]

Summary

Migration steps

1. Swap Hasura to use current_unified_fungible_asset_balances
   [We're here] 2. Add a killswitch on current_unified_fungible_asset_balances_to_be_renamed
   1. In addition, make a migration dropping columns. We want to split dropping columns separately from adding columns back so that we can add the columns without going through diesel migration again.
   2. Deploy the change with KS turned on. This should create no downtime since column dropping is quick.
2. Add generated columns back in dbeaver
3. Create new migration with added columns. Then remove KS.
   1. Also need to spin up backfill processor with KS turned off.
4. Swap Hasura to use current_unified_fungible_asset_balances_to_be_renamed

Backfill later

Devnet: 570187040
Testnet: 5776192143
Mainnet: 1660732247

Test

Confirmed that table is empty