remove traces of xamarin and specify sdk

src/iOS/Avalonia.iOS/Avalonia.iOS.csproj

@@ -1,8 +1,6 @@
-<Project>
-  <Import Project="Sdk.props" Sdk="Xamarin.Legacy.Sdk" />
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net6.0-ios</TargetFrameworks>
-    <TargetFrameworks Condition="'$(MSBuildRuntimeType)' != 'Core'">$(TargetFrameworks);xamarin.ios10</TargetFrameworks>
+    <TargetFramework>net6.0-ios</TargetFramework>
     <SupportedOSPlatformVersion>10.0</SupportedOSPlatformVersion>
     <MSBuildEnableWorkloadResolver>true</MSBuildEnableWorkloadResolver>
   </PropertyGroup>
@@ -10,8 +8,7 @@
     <ProjectReference Include="..\..\Avalonia.Base\Avalonia.Base.csproj" />
     <ProjectReference Include="..\..\Skia\Avalonia.Skia\Avalonia.Skia.csproj" />
   </ItemGroup>
-  <Import Project="Sdk.targets" Sdk="Xamarin.Legacy.Sdk" />
-
+  
   <!-- Workaround for https://github.com/dotnet/msbuild/issues/4584 -->
   <Target Name="_RemoveNativeReferencesManifest" AfterTargets="BuiltProjectOutputGroup">
     <ItemGroup>