do not set LXC default config

this was accidentally re-introduced in 7120fb4b

Signed-off-by: Evgeni Golov <evgeni@golov.de>

cloud/lxc/lxc_container.py

@@ -1684,7 +1684,6 @@ def main():
             ),
             config=dict(
                 type='path',
-                default='/etc/lxc/default.conf'
             ),
             vg_name=dict(
                 type='str',