[release/3.1] Remove Helix remnants (#39004)

Have no Helix jobs in any existing pipeline
- Helix mentions are just confusing here
- `tell-mode` because this cleanup affects only test and test asset projects.

Changes:
- remove Helix-related files
- clean out Helix mentions in miscellaneous files
- clean out Helix mentions in *.csproj files
- clean out Helix mentions in *.cs files

Author: dougbu

.azure/pipelines/helix-test.yml

@@ -1,5 +1,4 @@
 <Project>
-
   <PropertyGroup>
     <!-- Only build Microsoft.AspNetCore.App and ref/ assemblies in source build. -->
     <!-- Analyzer package are needed in source build for WebSDK -->
@@ -96,8 +95,6 @@
 
     <IsPackable Condition="'$(IsPackable)' == '' AND ('$(IsImplementationProject)' == 'true' OR '$(IsAnalyzersProject)' == 'true') ">true</IsPackable>
     <IsPackable Condition="'$(IsPackable)' == '' ">false</IsPackable>
-
-    <BuildHelixPayload Condition="'$(BuildHelixPayload)' == '' AND '$(IsTestProject)' == 'true'">true</BuildHelixPayload>
   </PropertyGroup>
 
   <PropertyGroup>
@@ -168,5 +165,4 @@
   <Import Project="eng\targets\Wix.Common.targets"  Condition="'$(MSBuildProjectExtension)' == '.wixproj'" />
   <Import Project="eng\targets\Npm.Common.targets"  Condition="'$(MSBuildProjectExtension)' == '.npmproj'" />
   <Import Project="eng\targets\ReferenceAssembly.targets" Condition=" $(HasReferenceAssembly) " />
-
 </Project>

Directory.Build.targets

@@ -9,4 +9,3 @@ IsPackable         | Set to `true` when the project should produce a package. Th
 IsShipping         | Set to `true` when the project output is intended for use by customers. Defaults to `true` for analyzer, implementation and specification test projects; `false` otherwise.
 IsShippingPackage  | Set to `true` when a package produced from project is intended for use by customers. Defaults to `IsShipping`. Note this may be `true` even for projects with `IsPackable` set to `false`.
 IsAspNetCoreApp    | Set to `true` when the assembly is part of the [Microsoft.AspNetCore.App shared framework](./SharedFramework.md) and is not available as a NuGet package (unless `IsPackable` is also set to `true` -- the default). Defaults to `false`.
-TestDependsOnMssql | Set to `true` when your tests depends on SQL Server. This will ensure distribute tests on Helix install LocalDB ([more information on Helix](./Helix.md)). Defaults to `false`.

docs/Helix.md

@@ -426,10 +426,6 @@
       <Uri>https://github.com/dotnet/arcade</Uri>
       <Sha>afb79612f8e0b62603d9c1a614d7e4cf3f54a1e7</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.Helix.Sdk" Version="2.0.0-beta.21552.6">
-      <Uri>https://github.com/dotnet/arcade</Uri>
-      <Sha>afb79612f8e0b62603d9c1a614d7e4cf3f54a1e7</Sha>
-    </Dependency>
     <Dependency Name="Microsoft.AspNetCore.Testing" Version="3.1.21-servicing.21522.3" CoherentParentDependency="Microsoft.EntityFrameworkCore">
       <Uri>https://dev.azure.com/dnceng/internal/_git/dotnet-extensions</Uri>
       <Sha>c7c07d575c22a9686fe9e07cda4d21cdd1151b33</Sha>