PR review feedback and build fix

src/System.Memory.Polyfill/System.Memory.Polyfill.csproj

@@ -4,15 +4,10 @@
     <Description>Adapters for Span APIs</Description>
     <TargetFrameworks>netstandard1.3;netcoreapp2.1</TargetFrameworks>
     <PackageTags>Span Memory Adapter</PackageTags>
-    <!-- disable automatic compile item inclusion so that we can set the correct metadata on TextTemplate-generated sources -->
-    <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
     <PackageReference Include="System.Buffers" Version="$(SystemMemoryVersion)" />
     <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="$(SystemCompilerServicesUnsafeVersion)" />
   </ItemGroup>
-  <ItemGroup>
-    <Compile Include="System\**\*.*" />
-  </ItemGroup>
 </Project>

tests/System.Memory.Polyfill.Tests/System.Memory.Polyfill.Tests.csproj

@@ -1,13 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Import Project="..\..\tools\common.props" />
   <PropertyGroup>
-    <TargetFrameworks>net46;netcoreapp2.1</TargetFrameworks>
-    <AssemblyOriginatorKeyFile>../../tools/test_key.snk</AssemblyOriginatorKeyFile>
-    <SignAssembly>true</SignAssembly>
-    <PublicSign Condition=" '$(OS)' != 'Windows_NT' ">true</PublicSign>
-    <Description></Description>
-    <Copyright>Microsoft Corporation, All rights reserved</Copyright>
-    <PackageRequireLicenseAcceptance>False</PackageRequireLicenseAcceptance>
+    <TargetFrameworks>netcoreapp2.1</TargetFrameworks>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(TargetsWindows)' == 'true'">
+    <TargetFrameworks>net46</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="xunit" Version="2.3.1" />