Sync shared code from runtime (#21866)

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Author: github-actions[bot]

src/Shared/runtime/Quic/Implementations/MsQuic/Internal/MsQuicApi.cs

@@ -142,8 +142,6 @@ static MsQuicApi()
             // - Otherwise, dial this in to reflect actual minimum requirements and add some sort of platform
             //   error code mapping when creating exceptions.
 
-            OperatingSystem ver = Environment.OSVersion;
-
             // TODO: try to initialize TLS 1.3 in SslStream.
 
             try