Remove SelfContained_R2R_Composite test and infrastructure

[Copilot]

Issue #54234 identified that building self-contained composite R2R apps cannot be properly supported in runtime repo test infrastructure. The test was disabled since introduction and SDK repo provides coverage.

cc @dotnet/appmodel

Changes

• Remove SelfContained_R2R_Composite test method marked with [ActiveIssue]
• Remove SelfContainedCompositeApp property and initialization from SharedTestState
• Remove disposal of SelfContainedCompositeApp

Total: 18 lines removed from BundledAppWithSubDirs.cs

Original prompt

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This section details on the original issue you should resolve

<issue_title>Need to find a way to build a self-contained composite r2r app in the context of Host/Bundle tests.</issue_title>
<issue_description>Right now an attempt to build a self-contained app as a part of Host/Bundle test fails. For the time being, if it is possible, we could use some workaround, but it is not yet clear if that is possible.

Our current test infrastructure emulates SDK environment and for composite r2r we would need to fake even more. It may be more feasible to create a test tool (like Bundler, but for building), that could allow just the scenarios in tests and with simpler setup.</issue_description>

<agent_instructions>We should remove the SelfContained_R2R_Composite test and corresponding SelfContainedCompositeApp in BundledAppWithSubDirs.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@ Tagging subscribers to this area: @agocke, @vitek-karas, @VSadov See info in [area-owners.md](https://github.com/dotnet/runtime/blob/main/docs/area-owners.md) if you want to be subscribed.

Issue Details

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Right now an attempt to build a self-contained app as a part of Host/Bundle test fails. The "right" fix for that may need to happen on SDK side.
For the time being, if it is possible, we could use some workaround, but it is not yet clear if that is possible.

Author:	VSadov
Assignees:	-
Labels:	area-Single-File, area-crossgen2-coreclr
Milestone:	-

@VSadov CC: @trylek - This is a bug to track enabling of singlefile composite r2r tests in runtime repo introduced in https://github.com//pull/53739 @agocke @VSadov was this completed? @elinor-fung I think trying to emulate all the combinations of how an app can be deployed in the SDK is a bit too complicated to be worth it in the runtime repo. It would likely be expensive and still not the 'real' scenario. We can rely on coverage in the sdk repo: https://github.com/dotnet/sdk/blob/dc026948482e5d42e34b9e565f113c9d814e180c/test/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishASingleFileApp.cs#L298

• Fixes Need to find a way to build a self-contained composite r2r app in the context of Host/Bundle tests. #54234

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[elinor-fung]

Should also reduce the amount of disk space we use during a test run - related: #120653

[Copilot]

Pull Request Overview

This PR removes the disabled SelfContained_R2R_Composite test and its associated infrastructure from the Bundle tests. The test was marked with [ActiveIssue] since introduction because building self-contained composite R2R apps cannot be properly supported in the runtime repo test infrastructure. Test coverage is provided by the SDK repo instead.

Key Changes:

• Removed SelfContained_R2R_Composite test method marked with [ActiveIssue]
• Removed SelfContainedCompositeApp property and all related code from SharedTestState