Add ObsoleteAttribute and EditorBrowsable(Never) to DynamicDependency.Condition

[jtschuster]

Based on dotnet/linker#1231, we decided to not actually implement what this property was intended for, and the implementation only supports "DEBUG" as the configuration. In GitHub search, I only see references to Condition in linker tests.

https://github.com/dotnet/runtime/blob/main/src/tools/illink/src/linker/Linker/DynamicDependency.cs#L111-L130

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[dotnet-policy-service]

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[stephentoub]

@terrajobst, do we need to review this?