Revert "Add auto update GitHub action"

The auto update is creating merge commits instead of rebasing, therefore
it is not the right choice.
This reverts commit 81a602dd71.

Signed-off-by: Till Maas <opensource@till.name>

.github/workflows/auto-update.yml

@@ -1,23 +0,0 @@
----
-name: Auto-update
-# Auto-update only listens to `push` events.
-# If a pull request is already outdated when enabling auto-merge, manually
-# click on the "Update branch" button a first time to avoid having to wait for
-# another commit to land on the base branch for the pull request to be updated.
-# on: push
-# If pull requests are always based on the same branches, only triggering the
-# workflow when these branches receive new commits will minimize the workflow
-# execution.
-on:
-  push:
-    branches:
-      - main
-
-jobs:
-  Auto:
-    name: Auto-update
-    runs-on: ubuntu-latest
-    steps:
-      - uses: tibdex/auto-update@v2
-        with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}