tests: fix ospf6_topo1_vrf

tests: fix ospf6_topo1_vrf

ospf6d (and all other daemons except zebra) doesn't correctly process
`interface X vrf Y`, because it doesn't know existing VRFs at the time
of configuration file reading. Therefore it doesn't apply configuration
provided in the interface node.

Fix the problem by removing `vrf Y` part, having just an interface name
is enough.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>