[ci, simulator] Drop nix installation

Nix don't need to be installed in a nixos machine.

Author: engdoreis

.github/workflows/ci.yml

@@ -59,13 +59,6 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
-    - name: Install Nix
-      uses: cachix/install-nix-action@v27
-      with:
-        extra_nix_config: |
-          substituters = https://nix-cache.lowrisc.org/public/ https://cache.nixos.org/
-          trusted-public-keys = nix-cache.lowrisc.org-public-1:O6JLD0yXzaJDPiQW1meVu32JIDViuaPtGDfjlOopU7o= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
-
     - name: Setup Cache
       if: github.event_name != 'pull_request'
       run: |

.github/workflows/site.yml

@@ -29,12 +29,6 @@ jobs:
       url: ${{ steps.deployment.outputs.page_url }}
     runs-on: nixos
     steps:
-      - name: Install Nix
-        uses: cachix/install-nix-action@v27
-        with:
-          extra_nix_config: |
-            substituters = https://nix-cache.lowrisc.org/public/ https://cache.nixos.org/
-            trusted-public-keys = nix-cache.lowrisc.org-public-1:O6JLD0yXzaJDPiQW1meVu32JIDViuaPtGDfjlOopU7o= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
       - name: Checkout
         uses: actions/checkout@v4
       - name: Build Documentation