Remove Internal.AspNetCore.Analyzers (#24693)

* Remove Internal.AspNetCore.Analyzers

This resolves build flakiness caused by referencing the analyzer:

```
2020-08-07T21:22:39.1149296Z ##[error].dotnet\sdk\5.0.100-rc.1.20379.10\Microsoft.Common.CurrentVersion.targets(4188,5): error MSB3026: (NETCORE_ENGINEERING_TELEMETRY=Build)
Could not copy "F:\workspace\_work\1\s\artifacts\obj\Internal.AspNetCore.Analyzers\Release\netstandard1.3\Internal.AspNetCore.Analyzers.dll"
to "F:\workspace\_work\1\s\artifacts\bin\Internal.AspNetCore.Analyzers\Release\netstandard1.3\Internal.AspNetCore.Analyzers.dll". Beginning retry 1 in 1000ms.
The process cannot access the file 'F:\workspace\_work\1\s\artifacts\bin\Internal.AspNetCore.Analyzers\Release\netstandard1.3\Internal.AspNetCore.Analyzers.dll' because it is being used by another process.
```

The analyzer checks if pubternal types are being exposed in public APIs. We no longer author pubternal types, so this is no longer a concern.

* Remove DisablePubternalApiCheck

Author: pranavkm

Directory.Build.props

@@ -140,20 +140,6 @@
     <InternalInstallerBaseName>$(RuntimeInstallerBaseName)-internal</InternalInstallerBaseName>
   </PropertyGroup>
 
-  <ItemGroup
-    Condition="'$(DisablePubternalApiCheck)' != 'true'
-      AND '$(IsTestProject)' != 'true'
-      AND '$(IsBenchmarkProject)' != 'true'
-      AND '$(IsTestAssetProject)' != 'true'
-      AND '$(MSBuildProjectName)' != 'Internal.AspNetCore.Analyzers'
-      AND '$(MSBuildProjectExtension)' == '.csproj'">
-    <ProjectReference
-      Include="$(RepoRoot)src\Analyzers\Internal.AspNetCore.Analyzers\src\Internal.AspNetCore.Analyzers.csproj"
-      ReferenceOutputAssembly="false"
-      OutputItemType="Analyzer"
-      PrivateAssets="All" />
-  </ItemGroup>
-
   <!-- Compilation options which apply to all languages. Language-specific options should be set in eng/targets/$(lang).Common.props -->
   <PropertyGroup>
     <BuildArchitecture>$([System.Runtime.InteropServices.RuntimeInformation]::ProcessArchitecture.ToString().ToLowerInvariant())</BuildArchitecture>