Remove new platform members from OSPlatform

[adamsitnik]

The spec mentions removing also the "Browser": #40111 (comment)

I am not sure about this since it was added 4 months ago together with Architecture.Wasm in #34781

cc @terrajobst

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[adamsitnik]

I've added the no merge label as I simply need to revert more changes (new methods added to RuntimeInformation && OrdinalIgnoreCaseChange)

[jeffhandley]

@terrajobst / @adamsitnik -- I propose that we leave OSPlatform.Browser in place for this PR since there are already some references to it in some of our tests. We'd then keep this PR to reverting @adamsitnik's PR that had added the other members and changed the string comparison.

Here are a couple of PRs that had added references to OSPlatform.Browser:

1. PR Fix creating OperatingSystem with PlatformID.Other #39130
2. PR WASM: Fix System.IO.MemoryMappedFiles tests #39355

I was considering a suggestion that we change the reference to OSPlatform.Browser to use OperatingSystem.IsBrowser(), but the references to OSPlatform.Browser in those files is alongside other OSPlatform references, which would make the work snowball.

[steveisok]

I would definitely feel more comfortable if we left OSPlatform.Browser in place. Snowballs at this point in time would be pretty bad.

[akoeplinger]

I don't think it's that bad, there are only two usages of OSPlatform.Browser outside of the RuntimeInformation tests. We can trivially change those.

[campersau]

Note that aspnetcore is also already using OSPlatform.Browser: https://github.com/search?l=C%23&p=1&q=%22osplatform.browser%22&type=Code

[akoeplinger]

Yeah we can change them back to using RuntimeInformation.IsOSPlatform(OSPlatform.Create("BROWSER")). I'd still prefer that to releasing with a new property that we immediately obsolete.

[adamsitnik]

@buyaa-n@jeffhandley PTAL. I've removed the methods and properties that I've recently added.

Once #40457 gets merged I am going to send another PR that will make RuntimeInfromation.IsOSPlatform just call OperatingSystem.IsOSPlatform, remove Browser and use new OperatingSystem methods everywhere in runtime and aspnet

[buyaa-n]

LGTM, thanks!

[lewing]

We'll need to fix dotnet/aspnetcore as well https://github.com/dotnet/aspnetcore/search?q=OSPlatform.Browser&unscoped_q=OSPlatform.Browser

[adamsitnik]

The CI failure is unrelated (Utf8String long running test timeout), merging

[adamsitnik]

I've sent a PR to ASP.NET: dotnet/aspnetcore#24652

/cc @jeffhandley@eerhardt