Remove zuul-stream-functional-2.7

We have removed support for Ansible 2.7 so we should remove the
zuul-stream-functional-2.7 job as well.

Change-Id: If6657c8392ab55052a2fd9981e5d333c254dfbae

.zuul.yaml

@@ -27,15 +27,6 @@
       - zuul/lib/ansible*
       - playbooks/zuul-stream/.*
 
-- job:
-    name: zuul-stream-functional-2.7
-    parent: zuul-stream-functional
-    # Force executor to use same Ansible version as "controller" node so
-    # that the inventory.yaml file will be correct for that version.
-    ansible-version: 2.7
-    vars:
-      zuul_ansible_version: 2.7
-
 - job:
     name: zuul-stream-functional-2.8
     parent: zuul-stream-functional