Updated langversion to 8.0 (dotnet#4687)

* Updated langversion

* Removed comment and other places where LangVersion was being set explicitly

* Moved LangVersion for fsproj to Directory.Build.props

Author: harishsk

Directory.Build.props

@@ -92,7 +92,8 @@
 
   <!-- Language configuration -->
   <PropertyGroup>
-    <LangVersion>latest</LangVersion> <!-- default to allowing all language features -->
+    <LangVersion Condition="'$(MSBuildProjectExtension)'=='.csproj'">8.0</LangVersion>
+    <LangVersion Condition="'$(MSBuildProjectExtension)'=='.fsproj'">4.7</LangVersion>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   </PropertyGroup>
 

src/Microsoft.ML.CpuMath/Microsoft.ML.CpuMath.csproj

@@ -5,7 +5,6 @@
     <IncludeInPackage>Microsoft.ML.CpuMath</IncludeInPackage>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <DefineConstants>$(DefineConstants);CPUMATH_INFRASTRUCTURE</DefineConstants>
-    <LangVersion>7.3</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

test/Microsoft.ML.Benchmarks/Microsoft.ML.Benchmarks.csproj

@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <LangVersion>8.0</LangVersion>
     <GenerateProgramFile>false</GenerateProgramFile>
   </PropertyGroup>
   <ItemGroup>

test/Microsoft.ML.CpuMath.PerformanceTests/Microsoft.ML.CpuMath.PerformanceTests.csproj

@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk" ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <LangVersion>7.2</LangVersion>
     <GenerateProgramFile>false</GenerateProgramFile>
     <TargetFramework>netcoreapp3.0</TargetFramework>
     <!--