Remove the passing of nix cache creds.

There is no way to include them when fetching from a substituter.

.webhook_bridge/pipeline-build-homepage-staging.yaml

@@ -142,8 +142,6 @@ spec:
               - "type=registry,ref=$(params.image-name):buildcache,mode=max,compression=zstd,compression-level=22,rewrite-timestamp=true,image-manifest=true,oci-mediatypes=true"
               - --opt
               - build-arg:SOURCE_DATE_EPOCH=$(tasks.get-git-commit-time.results.unix-time)
-              - --secret
-              - id=cache_token,src=/workspace/nix-cache-creds/CACHE_GET_TOKEN
           - name: BUILDKITD_TOML
             value: |
               debug = true
@@ -157,8 +155,6 @@ spec:
             workspace: git-source
           - name: dockerconfig
             workspace: docker-credentials
-          - name: nix-cache-creds
-            workspace: nix-cache-creds
         runAfter:
           - fetch-repository
     finally:
@@ -223,7 +219,6 @@ spec:
     workspaces:
       - name: git-source
       - name: docker-credentials
-      - name: nix-cache-creds
   workspaces:
     - name: git-source
       volumeClaimTemplate:
@@ -238,9 +233,6 @@ spec:
     - name: docker-credentials
       secret:
         secretName: harbor-plain
-    - name: nix-cache-creds
-      secret:
-        secretName: nix-pull-through-cache
   params:
     - name: image-name
       value: "harbor.fizz.buzz/private/homepage-staging"