modules/installation-creating-gcp-worker: Drop 'region' from YAML
modules/installation-creating-gcp-worker: Drop 'region' from YAML

The script consuming the YAML landed without 'region' consumers in
bd08aca0cd (Add GCP UPI install docs, 2019-10-03, #17043), and still
has no consumers for that property.

vikram-redhat/openshift-docs,vikram-redhat/openshift-docs,vikram-redhat/openshift-docs,vikram-redhat/openshift-docs,vikram-redhat/openshift-docs