Resolve duplicate 'vars' key warning

Ansible showed the following warning:

While constructing a mapping from /var/lib/zuul/builds/071fbb91f78b4
0e69d63dff011a965a4/untrusted/project_0/softwarefactory-project.io/software-
factory/sf-operator/playbooks/run-tests.yaml, line 2, column 3, found a
duplicate dict key (vars). Using last defined value only.

- playbooks/run-tests.yaml: Fix duplicated `vars:` section.

Change-Id: I2be501e4ac172dc8f29ba3858053db48f5c8231f

Author: calancha

playbooks/run-tests.yaml

@@ -2,7 +2,6 @@
 - hosts: "{{ hostname | default('controller') }}"
   vars:
     mode: standalone
-  vars:
     project_dir: "{% if zuul.project.src_dir is defined %}~/{{ zuul.project.src_dir }}{% else %}..{% endif %}"
   pre_tasks:
     - name: Install test dependencies