[WIP] Remove obsolete API marked in .NET 8

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Remove API that was marked obsolete in <= .NET 8</issue_title>
<issue_description>It's been since #27529 that we did a global pass to remove API that was marked Obsolete long enough ago. A good definition of long enough ago is "shipped in the last LTS" ie., .NET 8.0, since then even customers that only consume LTS will have had a chance to see the Obsolete attribute.

In a simple grep of release/8.0 vs main, I see roughly 140 that meet this criteria. Probably easiest to do this in chunks by folder.</issue_description>

<agent_instructions>Analyze the obsoletion marks in the repository and check git blame for each of them to collect a report that would contain the table with information when the obsoletion was introduced (date of the commit merged into main) and sort it from the oldest to the newest? Your PR should contain a document in the root of the repository with this table. Do not change any code.</agent_instructions>

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

@danmoseley rough grep and diff gave this, with line numbers mostly as of now https://gist.github.com/danmoseley/e5aed5508af95e8d455cf34f3d90e846

Fixes #62867

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[ilonatommy]

Totally misunderstood the prompt.