isisd: fix wrong check for MT commands

isisd: fix wrong check for MT commands

```
anlan# show run
!
interface eth0
 ip router isis A
exit
!
router isis A
 metric-style narrow <- NOT wide
exit
!
end
anlan (config)# int eth0
anlan (config-if)# no isis topology ipv6-unicast
% Configuration failed.

Error type: validation
Error description: Multi topology IS-IS can only be used with wide metrics
```

The MT commands are mainly controlled by the binded area, not by interface.
Currently if there is any MT configuration in the area, `metric-style` must
be with the `wide` mode, this requirement is sufficient.  So, the
unnecessary/wrong check for MT in the interface should be removed.

Signed-off-by: anlan_cs <anlan_cs@126.com>