Remove ExportAvaloniaModuleAttribute .

This feature is no longer supported.

src/Avalonia.Controls/Platform/ExportAvaloniaModuleAttribute.cs

@@ -1,58 +0,0 @@
-using System;
-
-namespace Avalonia.Platform
-{
-    /// <summary>
-    /// Defines an "Avalonia Module", a 3rd party extension to Avalonia that can be automatically initialized by an AppBuilder instance.
-    /// </summary>
-    /// <remarks>
-    /// Avalonia Modules can either be platform independent (ex default control styles provider) or dependent on a
-    /// specific windowing or rendering subsystem being used (ex native rendering speedup, subsystem-specific interop backends).
-    /// In the case of a subsystem-specific module, you can specify multiple module implementations, and also a fallback
-    /// platform-independent module if you so choose. Additionally, these different implementations can be in different assemblies.
-    /// They just need to all share the same module name.
-    /// 
-    /// For example, if I had a module Foo that has a special back-end for Skia and a less performant/less user friendly back-end for
-    /// any other rendering subsystem, I would do the following:
-    /// <code>
-    /// // In assembly FooModuleSkia.dll
-    /// [assembly:ExportAvaloniaModule("Foo", typeof(FooModuleSkia), ForRenderingSubsystem="Skia")]
-    /// 
-    /// class FooModuleSkia
-    /// {
-    ///     public FooModuleSkia()
-    ///     {
-    ///         InitializeModule();
-    ///     }
-    /// }
-    /// 
-    /// // In assembly FooModuleFallback.dll
-    /// [assembly:ExportAvaloniaModule("Foo", typeof(FooModuleFallback))]
-    /// 
-    /// class FooModuleFallback
-    /// {
-    ///     public FooModuleFallback()
-    ///     {
-    ///         InitializeModule();
-    ///     }
-    /// }
-    /// 
-    /// </code>
-    /// The fallback module will only be initialized if the Skia-specific module is not applicable.
-    /// </remarks>
-    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
-    public sealed class ExportAvaloniaModuleAttribute : Attribute
-    {
-        public ExportAvaloniaModuleAttribute(string name, Type moduleType)
-        {
-            Name = name;
-            ModuleType = moduleType;
-        }
-
-        public string Name { get; private set; }
-        public Type ModuleType { get; private set; }
-
-        public string ForWindowingSubsystem { get; set; } = "";
-        public string ForRenderingSubsystem { get; set; } = "";
-    }
-}