[PROTOTYPE] Remove custom sparse-checkouts for built-in checkout task

[Alan Zimmer (alzimmermsft)]

Description

Investigates removing some of the custom sparse-checkout operations with the built-in checkout task's sparse-checkout.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

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