remove C# pre-build steps from prepare_build_windows.bat

tools/internal_ci/helper_scripts/prepare_build_windows.bat

@@ -58,26 +58,9 @@ ccache --version
 
 @rem Only install C# dependencies if we are running C# tests
 If "%PREPARE_BUILD_INSTALL_DEPS_CSHARP%" == "true" (
-  @rem C# prerequisites: Install dotnet SDK
-  powershell -File src\csharp\install_dotnet_sdk.ps1 || goto :error
-
-  @rem Explicitly add default nuget source.
-  @rem (on Kokoro grpc-win2016 workers, the default nuget source is not configured,
-  @rem which results in errors when "dotnet restore" is run)
-  %LOCALAPPDATA%\Microsoft\dotnet\dotnet nuget add source https://api.nuget.org/v3/index.json -n "nuget.org"
+  @rem Nothing to do here. C# has been removed from this repository.
 )
 
-@rem Add dotnet on path and disable some unwanted dotnet
-@rem option regardless of PREPARE_BUILD_INSTALL_DEPS_CSHARP value.
-@rem Always setting the env vars is fine since its instantaneous,
-@rem it can't fail and it avoids possible issues with
-@rem "setlocal" and "EnableDelayedExpansion" which would be required if
-@rem we wanted to do the same under the IF block.
-set PATH=%LOCALAPPDATA%\Microsoft\dotnet;%PATH%
-set NUGET_XMLDOC_MODE=skip
-set DOTNET_SKIP_FIRST_TIME_EXPERIENCE=true
-set DOTNET_CLI_TELEMETRY_OPTOUT=true
-
 @rem Only install Python interpreters if we are running Python tests
 If "%PREPARE_BUILD_INSTALL_DEPS_PYTHON%" == "true" (
   echo "!TIME!: invoking install_python_interpreters.ps1"