Use a dedicated ScriptDeath type to signal script termination instead of WorkerScript

Problem with throwing WorkerScript is that the termination signal object can pass
through user code, which permits user to modify that object and all parts of the
game state accessible through it.

src/NetscriptFunctions/Corporation.ts

@@ -637,9 +637,6 @@ export function NetscriptCorporation(
       const office = getOffice(divisionName, cityName);
       if (!Object.values(EmployeePositions).includes(job)) throw new Error(`'${job}' is not a valid job.`);
       return netscriptDelay(1000, workerScript).then(function () {
-        if (workerScript.env.stopFlag) {
-          return Promise.reject(workerScript);
-        }
         return Promise.resolve(office.setEmployeeToJob(job, amount));
       });
     },