Use named export of MessageUtility in Scheduler.ts
import = require('…') should only be used when the required module exports via the respective
export = instruction.
As MessageUtility exports only one named export (called `MessageUtility`), we should import via ES6 named import syntax.
Note: Technically (in the generated source) this change makes no difference, as the named export was available as property, and therefore `import = ` worked.
Therefore there will be no changes required to the generated source codes.