remove github ci

.github/workflows/nix-build.yml

@@ -1,36 +0,0 @@
-name: "Nix Build"
-on:
-  pull_request:
-  push:
-    branches: [development, master]
-jobs:
-  build:
-    name: ${{ matrix.attribute }} / ${{ matrix.os }}
-    runs-on: ${{ matrix.os }}
-    strategy:
-      fail-fast: false
-      matrix:
-        os:
-          - ubuntu-latest
-        attribute:
-          - .#devShells.x86_64-linux.default
-          - .#packages.x86_64-linux.default
-          - .#checks.x86_64-linux.pre-commit
-    steps:
-    - uses: actions/checkout@v2.5.0
-    - uses: cachix/install-nix-action@v18
-      with:
-        extra_nix_config: |
-          access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
-    - name: free disk space
-      run: |
-        if [[ "${{matrix.os}}" == "ubuntu-latest" ]]
-        then
-          sudo rm -rf /opt
-        fi
-    - uses: cachix/cachix-action@v11
-      with:
-        name: feedback
-        extraPullNames: validity,safe-coloured-text,sydtest,autodocodec
-        signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
-    - run: nix build "${{matrix.attribute}}"