Remove AUTHORINO_IMAGE parameter from the OpenShift tutorial

The specific Authorino image tag used in this tutorial is tied to
version of the CRD installed and therefore it must be fixed in the
manifests (hosted elsewhere), rather than set through a parameter.

docs/tutorials/openshift-demo/README.md

@@ -54,7 +54,6 @@ Follow the instructions below to deploy the stack of resources and applications
     ```sh
     $ export OPENSHIFT_TOKEN=my-openshift-access-token \
              AUTHORINO_NAMESPACE=authorino-demo \
-             AUTHORINO_IMAGE=quay.io/3scale/authorino:20210415 \
              TALKER_API_HOST=talker-api.apps.my-openshift-server
     ```
 
@@ -73,7 +72,7 @@ Follow the instructions below to deploy the stack of resources and applications
 5. Patch the resources replacing the parameters to your env values:
 
    ```sh
-   $ sed -i -e "s/\${AUTHORINO_NAMESPACE}/$AUTHORINO_NAMESPACE/g;s/\${AUTHORINO_IMAGE}/$(print $AUTHORINO_IMAGE | sed -e 's/\//\\\//g')/g;s/\${TALKER_API_HOST}/$(print $TALKER_API_HOST | sed -e 's/\./\\\./g')/g" *.yaml
+   $ sed -i -e "s/\${AUTHORINO_NAMESPACE}/$AUTHORINO_NAMESPACE/g;s/\${TALKER_API_HOST}/$(print $TALKER_API_HOST | sed -e 's/\./\\\./g')/g" *.yaml
    ```
 
 6. Deploy Authorino: