Remove OSPlatformAttribute attributes from wasm linked output

[marek-safar]

Fixes #40163

[Dotnet-GitSync-Bot]

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[eerhardt]

Were you able to measure if this has any discernible impact on size in a Blazor wasm application? My assumption would be that it doesn't, since we have only annotated 2 types of APIs with these attributes so far:

1. Windows only - which should never get called in a Blazor WASM app.
2. UnsupportedOSPlatform("browser") - which also should never get called in a WASM app.

I was thinking this would more affect Xamarin since there we have APIs that are iOS or Android specific, and the application would actually call those APIs.

[marek-safar]

@eerhardt yeah, for the ideal app UnsupportedOSPlatformAttribute should have no effect on the final size as APIs which throw PNSE should not be reachable (and linked away) for such configuration but I don't think we can guarantee that.

The case for SupportedOSPlatformAttribute is simpler and we should just remove it all the time.

[marek-safar]

/backport to release/5.0-rc2

[github-actions]

Started backporting to release/5.0-rc2: https://github.com/dotnet/runtime/actions/runs/238084971