Dropped extra interfaces_info attribute from routers_info module

routers_info's interfaces_info attribute is not provided by
openstacksdk, it is added to each router resource by the routers_info
module after retrieving the routers list. To get the required data
list_router_interfaces() [1] is being called for each router resource
which then retrieves all ports for each router. This requires extra
api calls which might be useless because we do not know whether the
user actually cares about the ports. For getting ports of a router
we have the openstack.cloud.ports module. So instead of proactively
retrieving the router ports we drop the interfaces_info attribute.

The interfaces_info attribute was introduced because retrieving
interfaces via openstacksdk and openstack.cloud modules was
complex in the past [2]. Nowadays, using openstack.cloud.ports
Ansible and Jinja2 filters retrieving ip addresses of a router
is straight forward. In case someone still needs the old
interfaces_info attribute, one can refer to the module example
to see how it could be reproduced. But in general, retrieving the
router interfaces is much easier as can be seen in the updated
integration tests.

[1] https://opendev.org/openstack/openstacksdk/src/commit/3f81d0001dd994cde990d38f6e2671ee0694d7d5/openstack/cloud/_network.py#L1926
[2] https://review.opendev.org/c/openstack/ansible-collections-openstack/+/703927/6/plugins/modules/os_routers_info.py

Change-Id: I7fbdf11d07c95421d3aee800bfeebb88ea829817