Cleanup old configuration in readme (#133)

Co-authored-by: Fabian Amhof <[email protected]>

README.md

@@ -50,13 +50,5 @@ The following example shows the container used for linting the repository:
 | 0.43.0   | [markdownlint-cli 0.43.0](https://github.com/igorshubovych/markdownlint-cli/releases/tag/v0.42.0) | node:22.11.0-bookworm-slim | 0.43.0           | ![Docker Image Size (tag)](https://img.shields.io/docker/image-size/swissgrc/azure-pipelines-markdownlint/0.43.0?style=flat-square)   |
 <!-- markdownlint-restore -->
 
-### Configuration
-
-These environment variables are supported:
-
-| Environment variable   | Default value        | Description                                                      |
-|------------------------|----------------------|------------------------------------------------------------------|
-| MARKDOWNLINT_VERSION   | `0.39.0`             | Version of markdownlint-cli installed in the image.              |
-
 [markdownlint]: https://github.com/igorshubovych/markdownlint-cli
 [Azure Pipelines container jobs]: https://docs.microsoft.com/en-us/azure/devops/pipelines/process/container-phases