Drop opentack_version from oscore-test-cookiecutter-model job

The parameter is explicitly set in the context file which is
mandatory for job. Avoid accidental override by removing
openstack_version from COOKIECUTTER_EXTRA_CONTEXT

Change-Id: I6f26ed1961ef1919ee16f5c02bddf52d8ad47406
diff --git a/jenkins/client/job/oscore/cookiecutter.yml b/jenkins/client/job/oscore/cookiecutter.yml
index f38609a..bc180b4 100644
--- a/jenkins/client/job/oscore/cookiecutter.yml
+++ b/jenkins/client/job/oscore/cookiecutter.yml
@@ -66,7 +66,6 @@
                   cookiecutter_template_branch: 'master'
                   shared_reclass_url: https://gerrit.mcp.mirantis.net/salt-models/reclass-system.git
                   shared_reclass_branch: 'master'
-                  openstack_version: pike
             STACK_INSTALL:
               type: string
               default: 'core,openstack,ovs'