Remove redundant #if NET directives from .NET-only files (#118424)

Author: Copilot

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HuffmanDecodingException.cs

@@ -19,26 +19,20 @@ public HuffmanDecodingException(string message)
         {
         }
 
-#if NET
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
-#endif
         private HuffmanDecodingException(SerializationInfo info, StreamingContext context)
             : base(info, context)
         {
         }
 
-#if NET
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
-#endif
         void ISerializable.GetObjectData(SerializationInfo serializationInfo, StreamingContext streamingContext)
         {
             base.GetObjectData(serializationInfo, streamingContext);
         }
 
-#if NET
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
         [EditorBrowsable(EditorBrowsableState.Never)]
-#endif
         public override void GetObjectData(SerializationInfo serializationInfo, StreamingContext streamingContext)
         {
             base.GetObjectData(serializationInfo, streamingContext);

src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackDecodingException.cs

@@ -21,9 +21,7 @@ public QPackDecodingException(string message, Exception innerException) : base(m
         {
         }
 
-#if NET
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
-#endif
         private QPackDecodingException(SerializationInfo info, StreamingContext context) : base(info, context)
         {
         }

src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackEncodingException.cs

@@ -18,9 +18,7 @@ public QPackEncodingException(string message, Exception innerException)
         {
         }
 
-#if NET
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
-#endif
         private QPackEncodingException(SerializationInfo info, StreamingContext context) : base(info, context)
         {
         }

src/libraries/Common/src/System/Net/NetworkInformation/NetworkInformationException.cs

@@ -35,10 +35,8 @@ public NetworkInformationException(int errorCode) : base(errorCode)
         {
         }
 
-#if NET
         [Obsolete(Obsoletions.LegacyFormatterImplMessage, DiagnosticId = Obsoletions.LegacyFormatterImplDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
         [EditorBrowsable(EditorBrowsableState.Never)]
-#endif
         protected NetworkInformationException(SerializationInfo serializationInfo, StreamingContext streamingContext) : base(serializationInfo, streamingContext)
         {
         }

src/libraries/System.Security.Permissions/ref/System.Security.Permissions.netcoreapp.cs

@@ -6,9 +6,7 @@
 
 namespace System.Xaml.Permissions
 {
-#if NET
     [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
-#endif
     public sealed partial class XamlLoadPermission : System.Security.CodeAccessPermission, System.Security.Permissions.IUnrestrictedPermission
     {
         public XamlLoadPermission(System.Collections.Generic.IEnumerable<System.Xaml.Permissions.XamlAccessLevel> allowedAccess) { }

src/libraries/System.Text.Json/ref/System.Text.Json.netcoreapp.cs

@@ -12,10 +12,8 @@ public static partial class JsonMetadataServices
         public static System.Text.Json.Serialization.JsonConverter<System.Half> HalfConverter { get { throw null; } }
         public static System.Text.Json.Serialization.JsonConverter<System.TimeOnly> TimeOnlyConverter { get { throw null; } }
 
-#if NET
         public static System.Text.Json.Serialization.JsonConverter<System.Int128> Int128Converter { get { throw null; } }
         [System.CLSCompliantAttribute(false)]
         public static System.Text.Json.Serialization.JsonConverter<System.UInt128> UInt128Converter { get { throw null; } }
-#endif
     }
 }