delete old CI workflow

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/build.yaml

@@ -1,17 +0,0 @@
-name: build
-on:
-  push:
-  pull_request:
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    container:
-      image: ghcr.io/catthehacker/ubuntu:runner-latest
-    steps:
-      - uses: actions/checkout@v3
-      - uses: cachix/install-nix-action@v27
-      - name: run flacke check
-        run: nix flake check
-      - name: build packages
-        run: ./scripts/build-all.sh