Clean up test code after new .NET 10 AOT image approach

After the following changes, there is lots of test code that can be cleaned up/reorganized.

- https://github.com/dotnet/dotnet-docker/discussions/6312
- https://github.com/dotnet/dotnet-docker/pull/6352
- https://github.com/dotnet/dotnet-docker/pull/6358

Here's a quick summary of what I could see.

AOT test data is based on runtime-deps images. It should be based on the SDK images instead now.

https://github.com/dotnet/dotnet-docker/blob/bffebfd7c236ad2ed58e40ed8a155e936dd0c15c/tests/Microsoft.DotNet.Docker.Tests/TestData.cs#L229-L232

The AOT test scenarios should be moved to the SDK tests class:

https://github.com/dotnet/dotnet-docker/blob/bffebfd7c236ad2ed58e40ed8a155e936dd0c15c/tests/Microsoft.DotNet.Docker.Tests/RuntimeDepsImageTests.cs#L61-L75

`ProductImageData.SdkImageVariant` is no longer necessary (its purpose can be covered by just the regular `ImageVariant` property):

https://github.com/dotnet/dotnet-docker/blob/bffebfd7c236ad2ed58e40ed8a155e936dd0c15c/tests/Microsoft.DotNet.Docker.Tests/ProductImageData.cs#L34-L35

This workaround can be removed:

https://github.com/dotnet/dotnet-docker/blob/bffebfd7c236ad2ed58e40ed8a155e936dd0c15c/tests/Microsoft.DotNet.Docker.Tests/TestDataTests.cs#L53-L66

All runtime deps AOT special cases can be removed:

https://github.com/dotnet/dotnet-docker/blob/bffebfd7c236ad2ed58e40ed8a155e936dd0c15c/tests/Microsoft.DotNet.Docker.Tests/RuntimeDepsImageTests.cs#L49-L54

https://github.com/dotnet/dotnet-docker/blob/bffebfd7c236ad2ed58e40ed8a155e936dd0c15c/tests/Microsoft.DotNet.Docker.Tests/RuntimeDepsImageTests.cs#L26-L27