Remove NSX 'service' plugin

Remove NSX 'service' plugin

Following the spin-off for Neutron advanced services, this plugin
has become non-functional.
This patch removes the plugin, the service drivers, the database
models which kept tracking of resource associations, exceptions,
and obviously unit tests.

As there were some extensions which were leveraged only by this
plugin, they are being removed as well. In particular, one of
these extensions, 'routed-service-insertion' was in the
neutron.extensions package rather than neutron.plugins.vmware
package. This was for historical reasons. As no other plugin is
using this extension, it is being removed as well with this
patch.

By removing this plugin vmware the temporary skips applied to
neutron unit tests can be lifted. This patch does this.

Closes-Bug: #1403585

Change-Id: I0717f955b0f787c2951cb9db44ea5decc5d3dff0