Remove directly reference to System.Threading

Author: Tasteful

src/AutoMapper.Collection/AutoMapper.Collection.csproj

@@ -25,12 +25,4 @@
     <Reference Include="Microsoft.CSharp" />
   </ItemGroup>
 
-  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard1.1' ">
-    <PackageReference Include="System.Threading" Version="4.0.11" />
-  </ItemGroup>
-
-  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard1.3' ">
-    <PackageReference Include="System.Threading" Version="4.0.11" />
-  </ItemGroup>
-
 </Project>