basic: remove some extras

basic/infrastructure/namespaces/kustomization.yaml

----
-apiVersion: kustomize.config.k8s.io/v1beta1
-kind: Kustomization
-resources:
-  - stackspout.yaml

basic/overrides/cluster-issuer-staging.yaml

----
-apiVersion: cert-manager.io/v1
-kind: ClusterIssuer
-metadata:
-  name: letsencrypt-issuer-staging
-spec:
-  acme:
-    email: ${admin_email}
-    # overwrite this to "https://acme-staging-v02.api.letsencrypt.org/directory" for staging
-    server: "https://acme-staging-v02.api.letsencrypt.org/directory"
-    privateKeySecretRef:
-      # Secret resource used to store the account's private key.
-      name: letsencrypt-account-key
-    # Enable the HTTP01 challenge mechanism for this Issuer
-    solvers:
-    - http01:
-        ingress:
-          class: nginx

basic/overrides/stackspin-zulip-override.yaml

----
-apiVersion: v1
-kind: ConfigMap
-metadata:
-  namespace: stackspin-apps
-  name: stackspin-zulip-override
-data:
-  values.yaml: |
-    zulip:
-      environment:
-        SETTING_AUTHENTICATION_BACKENDS: '("zproject.backends.GenericOpenIdConnectBackend", "zproject.backends.EmailAuthBackend")'