Remove iohk hydra cache (#4861)

Looking htrough the build history, I can't find any builds going back 4
months or so that successfully pulled from this cache. They always retry
several times, then give up with a 530 error and move on.

Visiting the cache website, it also seems down as well.

Author: ehildenb

.github/workflows/release.yml

@@ -66,8 +66,8 @@ jobs:
           install_url: https://releases.nixos.org/nix/nix-2.30.1/install
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
-            substituters = http://cache.nixos.org https://hydra.iohk.io
-            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
+            substituters = http://cache.nixos.org
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
 
       - name: 'Install Cachix'
         if: ${{ !startsWith(matrix.os, 'self') }}
@@ -110,8 +110,8 @@ jobs:
           install_url: https://releases.nixos.org/nix/nix-2.30.1/install
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
-            substituters = http://cache.nixos.org https://hydra.iohk.io
-            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
+            substituters = http://cache.nixos.org
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
 
       - name: 'Install Cachix'
         if: ${{ !startsWith(matrix.os, 'self') }}

.github/workflows/test-pr.yml

@@ -166,8 +166,8 @@ jobs:
         with:
           install_url: https://releases.nixos.org/nix/nix-2.30.1/install
           extra_nix_config: |
-            substituters = http://cache.nixos.org https://hydra.iohk.io
-            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
+            substituters = http://cache.nixos.org
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
       - name: 'Install Cachix'
         uses: cachix/cachix-action@v14
         with:
@@ -202,8 +202,8 @@ jobs:
         with:
           install_url: https://releases.nixos.org/nix/nix-2.30.1/install
           extra_nix_config: |
-            substituters = http://cache.nixos.org https://hydra.iohk.io
-            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
+            substituters = http://cache.nixos.org
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
       - name: 'Install Cachix'
         if: ${{ !startsWith(matrix.os, 'self') }}
         uses: cachix/cachix-action@v14

.github/workflows/update-deps.yml

@@ -35,8 +35,8 @@ jobs:
           install_url: https://releases.nixos.org/nix/nix-2.30.1/install
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
-            substituters = http://cache.nixos.org https://hydra.iohk.io
-            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
+            substituters = http://cache.nixos.org
+            trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
 
       - name: 'Install Cachix'
         uses: cachix/cachix-action@v14