Remove provider router configuration

To be compatible with the Icehouse release of MidoNet, the
provider router configuration is removed from devstack since
it is no longer necessary to configure it.

Change-Id: I4be2d9bbf2c82fd375702cbb1d60c3277086134f
Implements: blueprint remove-provider-router-config-for-midonet
Merge "Remove provider router configuration"
Merge branch 'master' of https://github.com/openstack-dev/devstack