Fix broken links

[mccoyp]

Description

Resolves the errors reported by the aggregate-reports pipeline and also updates all references to the now-removed test proxy migration guide.

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.

[Copilot]

Pull Request Overview

This PR fixes broken documentation links throughout the Azure SDK for Python codebase by updating references from the removed test proxy migration guide to the current testing documentation. The changes ensure that developers can access accurate and up-to-date testing guidance.

• Updates all references from the deprecated test_proxy_migration_guide.md to the current tests.md documentation
• Removes obsolete migration guide references and cleanup instructions for inactive packages
• Fixes broken links that were causing pipeline failures in the aggregate-reports system

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tools/azure-sdk-tools/devtools_testutils/proxy_testcase.py	Removes migration guide comment and updates decorator documentation link
tools/azure-sdk-tools/devtools_testutils/proxy_fixtures.py	Updates fixture documentation link to current testing guide
tools/azure-sdk-tools/devtools_testutils/mgmt_recorded_testcase.py	Updates test class documentation link
tools/azure-sdk-tools/devtools_testutils/azure_recorded_testcase.py	Updates test class documentation link
tools/azure-sdk-tools/devtools_testutils/aio/proxy_testcase_async.py	Updates async decorator documentation link
sdk/webpubsub/azure-messaging-webpubsubservice/tests/STATE_OF_TESTS.md	Removes entire file containing outdated migration guide reference
sdk/batch/azure-batch/tests/decorators.py	Updates decorator documentation link
scripts/quickstart_tooling_dpg/template_tests/conftest.py	Updates sanitizer documentation link
doc/dev/mgmt/tests.md	Updates testproxy reference link
doc/dev/mgmt/multiapi.md	Updates example reference to use past tense for historical accuracy
doc/dev/mgmt/generating-integration-test.md	Simplifies documentation by removing outdated migration guide references