Fix runner integration test.

This test is broken, as it first sets environment variables, and then
immediately unsets it again.
This only worked by chance with the legacy tracer, and breaks the Lua
tracer.

.github/workflows/runner-checks.yml

@@ -167,7 +167,6 @@ jobs:
         shell: powershell
         run: |
           cat ./codeql-runner/codeql-env.sh | Invoke-Expression
-          $Env:CODEQL_EXTRACTOR_CSHARP_ROOT = "" # Unset an environment variable to make sure the tracer resists this
           & $Env:CODEQL_RUNNER dotnet build /p:UseSharedCompilation=false
 
       - name: Upload tracer logs