github: remove old flakehub workflow

.github/workflows/flakehub.yml

@@ -1,20 +0,0 @@
-name: "flakehub"
-on:
-  push:
-    branches:
-      - master
-jobs:
-  flakehub-publish:
-    runs-on: "ubuntu-latest"
-    permissions:
-      id-token: "write"
-      contents: "read"
-    steps:
-      - uses: "actions/checkout@main"
-      - uses: "DeterminateSystems/nix-installer-action@main"
-      - uses: "DeterminateSystems/flakehub-push@main"
-        with:
-          name: "alyraffauf/nixcfg"
-          rolling: true
-          visibility: "public"
-          include-output-paths: true