Revert "ci: add cachix build action"

This reverts commit b43cc04ea7.

.github/workflows/main.yml

@@ -1,18 +0,0 @@
-name: "Build and test"
-on:
-  pull_request:
-  push:
-jobs:
-  tests:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v4
-    - uses: cachix/install-nix-action@v25
-      with:
-        nix_path: nixpkgs=channel:nixos-unstable
-    - uses: cachix/cachix-action@v14
-      with:
-        name: liminalos
-        # If you chose API tokens for write access OR if you have a private cache
-        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-    - run: nix build