Remove unnecessary watcher_dashboard/models.py file
Remove unnecessary watcher_dashboard/models.py file

The django issue [1] have already fixed. So we can remove the file now.

[1] https://code.djangoproject.com/ticket/7198

Change-Id: Id25ad51cd69a2fe11067e706f5cfc8ed1b7e990f

openstack/watcher-dashboard,openstack/watcher-dashboard,openstack/watcher-dashboard,openstack/watcher-dashboard