Retire the README version bot

It fired on `release: published` and committed to main, the branch the
release points at its tag, so it could only ever leave main ahead of the
tag. release.sh now makes the same edit inside the release commit.

In this repo it was a no-op regardless: the pattern it rewrote does not
appear in this README, so it has been running and changing nothing.

.github/workflows/update-readme.yml

@@ -1,36 +0,0 @@
-name: Update README version
-
-on:
-  release:
-    types: [published]
-
-permissions:
-  contents: write
-
-jobs:
-  update:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v5
-        with:
-          ref: main
-          token: ${{ secrets.ORG_DISPATCH_TOKEN }}
-
-      - name: Update version in README
-        run: |
-          VERSION="${{ github.event.release.tag_name }}"
-          FILE="README.md"
-
-          # Update cargo dependency version (e.g. "0.2" -> "0.3")
-          MAJOR_MINOR="${VERSION#v}"
-          MAJOR_MINOR="${MAJOR_MINOR%.*}"
-          sed -i "s|libfreemkv = \"[0-9]*\.[0-9]*\"|libfreemkv = \"${MAJOR_MINOR}\"|" "$FILE"
-
-      - name: Commit and push
-        run: |
-          VERSION="${{ github.event.release.tag_name }}"
-          git config user.name "github-actions[bot]"
-          git config user.email "github-actions[bot]@users.noreply.github.com"
-          git add README.md
-          git diff --cached --quiet || git commit -m "Update to libfreemkv ${VERSION}"
-          git push