[cleanup] Remove unused package jest-mock-scheduler (#26084)

## Summary

Removing package jest-mock-scheduler introduced in PR
#14358, as it is no longer
referenced in the main branch code. The following files previously
referenced it:

- packages/scheduler/src/__tests__/Scheduler-test.js
- packages/scheduler/src/__tests__/SchedulerDOM-test.js
- packages/shared/__tests__/ReactDOMFrameScheduling-test.js
- scripts/jest/setupTests.js
- scripts/rollup/bundles.js

## How did you test this change?

ci green

Author: ymqy