restore Microsoft.DotNet.PlatformAbstraction dependency (#2043)

Author: adamsitnik

src/BenchmarkDotNet/BenchmarkDotNet.csproj

@@ -24,9 +24,9 @@
     <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.4" />
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="3.0.0" />
     <PackageReference Include="Microsoft.Diagnostics.Tracing.TraceEvent" Version="3.0.2" PrivateAssets="contentfiles;analyzers" />
+    <PackageReference Include="Microsoft.DotNet.PlatformAbstractions" Version="3.1.6" />
   </ItemGroup>
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
-    <PackageReference Include="Microsoft.DotNet.PlatformAbstractions" Version="3.1.6" />
     <PackageReference Include="Microsoft.Win32.Registry" Version="5.0.0" />
   </ItemGroup>
   <ItemGroup Condition="'$(OS)' == 'Windows_NT'">

src/BenchmarkDotNet/Portability/PlatformApis.cs

@@ -14,9 +14,7 @@
 using JetBrains.Annotations;
 using Microsoft.Win32;
 using static System.Runtime.InteropServices.RuntimeInformation;
-#if NETSTANDARD
 using RuntimeEnvironment = Microsoft.DotNet.PlatformAbstractions.RuntimeEnvironment;
-#endif
 
 namespace BenchmarkDotNet.Portability
 {
@@ -103,16 +101,8 @@ public static string GetOsVersion()
                     return OsBrandStringHelper.PrettifyMacOSX(systemVersion, kernelVersion);
             }
 
-            string operatingSystem;
-            string operatingSystemVersion;
-
-#if NETSTANDARD
-            operatingSystem = RuntimeEnvironment.OperatingSystem;
-            operatingSystemVersion = RuntimeEnvironment.OperatingSystemVersion;
-#else
-            operatingSystem = PlatformApis.GetOSName();
-            operatingSystemVersion = PlatformApis.GetOSVersion();
-#endif
+            string operatingSystem = RuntimeEnvironment.OperatingSystem;
+            string operatingSystemVersion = RuntimeEnvironment.OperatingSystemVersion;
 
             return OsBrandStringHelper.Prettify(
                 operatingSystem,