Per the latest version of the design, retryable internal transactions will run in internal sessions with lsid of the form (id, uid, txnNumber, txnUUID) as supposed to (id, uid, txnNumber, stmtId). So we should:

• Remove stmtId from the InternalSessionFields struct.
• Make getParentSessionId only check for txnUUID.
• Update unittests and jstests that use lsids of the form (id, uid, txnNumber, stmtId).