NSX: don't check router interface on network delete

[Salvatore Orlando]

since commit b50e66f the router interfaces will not be automatically delete anymore when a network is deleted.
Instead a 409 response code will be returned.

The NSX plugin still has logic to ensure correct backend state in case router interfaces are present on network_delete. This logic is useless and can be removed.
Also it performs some unnecessary queries, so it affects also plugin performance.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/105622

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/105622
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=ef3222d09030b5e25ed558179f9c7faab7f8e256
Submitter: Jenkins
Branch: master

commit ef3222d09030b5e25ed558179f9c7faab7f8e256
Author: Salvatore Orlando <email address hidden>
Date: Tue Jul 8 16:16:39 2014 -0700

    NSX: remove unnecessary checks on network delete

    Since commit b50e66f router interfaces are not deleted
    automatically when the network hosting them is deleted.

    The NSX plugin still has additional logic to ensure all the
    corresponding backend resources have been deleted as well.
    Such logic is now obsolete and can be removed. Moreover it
    also wasteful as it perform queries for retrieving NSX
    resource identifiers.

    This patch also amends a few related log statement to make
    them clearer.

    Change-Id: If3d8d98096a8363b216707f2558e37c80f58e515
    Closes-Bug: #1339401