chore(scheduler-alpha-and-scheduler-targets-alpha): remove alpha modules (#33951)

### Reason for this change

The aws-scheduler-alpha and aws-scheduler-targets-alpha modules have now been [stabilized](#33903) so we can delete the alpha modules. Also update any remaining references to these deprecated alpha modules.

### Description of changes

Removed `aws-scheduler-alpha` and `aws-scheduler-targets-alpha` modules from `@aws-cdk` package

### Description of how you validated changes

Ran `yarn install` and `npx lerna run build` successfully. Verified all integ tests are passing.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: gracelu0