Remove richnav pipeline and feed (#11682)

The service no longer exists.

Author: akoeplinger

NuGet.config

@@ -20,8 +20,6 @@
     <add key="vssdk-archived" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/vssdk-archived/nuget/v3/index.json" />
     <add key="vs-impl" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/vs-impl/nuget/v3/index.json" />
     <add key="vs-impl-archived" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/vs-impl-archived/nuget/v3/index.json" />
-    <!-- Used for the Rich Navigation indexing task -->
-    <add key="richnav" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/vs-buildservices/nuget/v3/index.json" />
     <!-- Used for BenchmarkDotNet prerelease packages -->
     <add key="benchmark-dotnet-prerelease" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/benchmark-dotnet-prerelease/nuget/v3/index.json" />
   </packageSources>
@@ -36,18 +34,12 @@
     <packageSource key="dotnet-core-internal-tooling">
       <package pattern="microsoft.*" />
     </packageSource>
-    <packageSource key="richnav">
-      <package pattern="richcodenav.envvardump" />
-    </packageSource>
   -->
   <packageSourceMapping>
     <clear />
     <packageSource key="dotnet-core-internal-tooling">
       <package pattern="microsoft.*" />
     </packageSource>
-    <packageSource key="richnav">
-      <package pattern="richcodenav.envvardump" />
-    </packageSource>
     <packageSource key="dotnet-eng">
       <package pattern="microsoft.*" />
       <package pattern="sn" />