ara_api role: We don't actually need run_once for sqlite migrations

In a previous patch we added a run_once so that many API servers don't
simultaneously run SQL migrations.
This is not relevant for sqlite because we're not dealing with a central
remote database server but instead a file on the local API server.

[1]: 41a1fd03f5

Change-Id: I5d6eb1808edfb93689486526602eb8a1b5007514

roles/ara_api/tasks/database_engine/django.db.backends.sqlite3.yaml

@@ -28,4 +28,3 @@
     ARA_SETTINGS: "{{ ara_api_settings }}"
     PATH: "{{ path_with_virtualenv | default('/usr/bin:/usr/local/bin') }}"
   command: ara-manage migrate
-  run_once: true