What is the difference between these ledger did files?

./ic/rs/rosetta-api/ledger_canister/ledger.did
./ic/rs/rosetta-api/ledger.did

which one is used for what purpose?

More specifically: what is the difference beteen account_balance and account_balance_dfx?

Also, why are we using the latter here: sdk/ledger.rs at master · dfinity/sdk · GitHub