Revert "Bring over NullableAttributes.cs"

This reverts commit 5d16c9c.

Author: jonathanpeppers

src-ThirdParty/System.Diagnostics.CodeAnalysis/NullableAttributes.cs

@@ -14,7 +14,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <OutputPath>$(MicrosoftAndroidSdkOutDir)</OutputPath>
     <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
-    <DefineConstants>$(DefineConstants);TRACE;HAVE_CECIL;MSBUILD;INTERNAL_NULLABLE_ATTRIBUTES;ANDROID_24;ANDROID_26;ANDROID_31</DefineConstants>
+    <DefineConstants>$(DefineConstants);TRACE;HAVE_CECIL;MSBUILD;ANDROID_24;ANDROID_26;ANDROID_31</DefineConstants>
     <AndroidGeneratedClassDirectory Condition=" '$(AndroidGeneratedClassDirectory)' == '' ">..\..\src\Mono.Android\obj\$(Configuration)\$(DotNetTargetFramework)\android-$(AndroidLatestStablePlatformId)\mcw</AndroidGeneratedClassDirectory>
     <NoWarn>8632</NoWarn>
     <SignAssembly>false</SignAssembly>
@@ -165,9 +165,6 @@
     <Compile Include="..\..\src-ThirdParty\StrongNameSigner\SigningHelper.cs">
       <Link>Utilities\%(Filename)%(Extension)</Link>
     </Compile>
-    <Compile Include="..\..\src-ThirdParty\System.Diagnostics.CodeAnalysis\NullableAttributes.cs">
-      <Link>Utilities\%(Filename)%(Extension)</Link>
-    </Compile>
   </ItemGroup>
 
   <ItemGroup>