[Store] Remove unreachable INVALID_BATCH_ID check after freeBatchID

[stmatengss]

Problem

In submitTransfer and mp_submitTransfer, after submission failure:

engine_.freeBatchID(batch_id);
return std::nullopt;
}

if (batch_id == INVALID_BATCH_ID) {  // ← unreachable dead code
    ...
}

batch_id is validated at function entry and cannot become INVALID_BATCH_ID between that guard and this check. The duplicate guard after the error-return path is never reached.

Fix

Remove both unreachable INVALID_BATCH_ID guards (one in submitTransfer, one in mp_submitTransfer).

Impact

• No behavior change (guards were never triggered)
• Eliminates misleading dead code