remove netstandard specific additions

Author: tonerdo

src/coverlet.core/coverlet.core.csproj

@@ -9,8 +9,6 @@
   <ItemGroup>
     <PackageReference Include="Mono.Cecil" Version="0.10.1" />
     <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
-    <PackageReference Include="System.Reflection.Metadata" Version="1.5.0" />
-    <PackageReference Include="System.Runtime.Extensions" Version="4.3.0" />
     <PackageReference Include="Microsoft.Extensions.FileSystemGlobbing" Version="2.0.1" />
   </ItemGroup>