Specify DebugType in directory.build.props

Enabled by https://github.com/dotnet/sdk/commit/24db8f1c96dc2857fcecce7f274f1aa94f0017f8

Ix.NET/Source/Directory.build.props

@@ -15,6 +15,7 @@
     <NoWarn>$(NoWarn);1701;1702;CS1591</NoWarn>
     <DefaultLanguage>en-US</DefaultLanguage>
     <IsTestProject>$(MSBuildProjectName.Contains('Test'))</IsTestProject>
+    <DebugType>embedded</DebugType>
   </PropertyGroup>
   
   <ItemGroup Condition="'$(IsTestProject)' != 'true' and '$(SourceLinkEnabled)' != 'false'">

Ix.NET/Source/System.Interactive/System.Interactive.csproj

@@ -6,7 +6,6 @@
     <Authors>Microsoft</Authors>
     <TargetFrameworks>net45;netstandard1.0</TargetFrameworks>
     <PackageTags>Ix;Interactive;Extensions;Enumerable</PackageTags>
-    <DebugType>embedded</DebugType>
   </PropertyGroup>
 
   <ItemGroup>