fix(scheduler-alpha): remove Group

[gracelu0]

Issue # (if applicable)

Closes #.

Reason for this change

Group was deprecated in favour of ScheduleGroup in #33678 - we want to remove the Group class altogether to keep the codebase clean and prevent additional breaking changes after graduation.

Description of changes

• delete Group file and unit test file
• replace any remaining usages of Group and group with ScheduleGroup and scheduleGroup

Describe any new or updated permissions being added

n/a

Description of how you validated changes

updated unit and integration tests

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

BREAKING CHANGE: Group has been removed. Use ScheduleGroup instead. In the Scheduleconstruct, use the scheduleGroup property instead of group to specify the schedule group.

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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

[aws-cdk-automation]

(This review is outdated)

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.38%. Comparing base (2623e00) to head (6f9df3a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #33823   +/-   ##
=======================================
  Coverage   82.38%   82.38%           
=======================================
  Files         120      120           
  Lines        6937     6937           
  Branches     1170     1170           
=======================================
  Hits         5715     5715           
  Misses       1119     1119           
  Partials      103      103           

Flag	Coverage Δ
suite.unit	82.38% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	∅ <ø> (∅)
packages/aws-cdk-lib/core	82.38% <ø> (ø)

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[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 6f9df3a
• Result: FAILED
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[gracelu0]

Closing as we will make this change in the stabilized module since the alpha modules will get deleted afterwards anyway.

[github-actions]

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