Fix broken links

[mccoyp]

Description

This fixes two broken links for azure-purview-sharing -- a PyPI aka.ms link appears to have been removed, and a broken ref docs link is replaced with an aka.ms link to the same docs that's used elsewhere.

One broken link came from the long-deprecated core/azure package: a migration guide from 2016 that no longer exists in the repo's wiki. Given the fact that the package is no longer used and the guide was almost a decade old, I removed the link and included a note to mention the docs being dropped.

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.

General Guidelines and Best Practices

• 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.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[mccoyp]

/check-enforcer override

[weshaggard]

@mccoyp I assume the failing purview pipeline will be addressed separately before their next release?

[mccoyp]

@weshaggard It looks like they'll need to address some things, yes. The Purview CI pipeline has been failing since it was apparently re-enabled in early September, unrelated to this PR.