Deleting port binding with neutron API

Issue

After a failed migration, there's some port bindings that might remain in the database. This can cause subsequent migrations to fails.

These errors are raised to nova with this error message:

2021-02-04 21:04:53.505 31 ERROR nova.network.neutronv2.api [req-d6c7bb0a-8fa0-4a86-960d-e1783f96da49 6e49802d3a6a4b14a73a49341f3cfb99 dad8018dc9944e15bbccc9315023ef71 - default default] [instance: 63069c5b-05c8-4c05-95ed-651764c0f9e7] Binding failed for port 710d70bd-597b-4f2c-8e71-796ebc36fead and host compute-1.redhat.local . Error: (409 {"NeutronError": {"type": "PortBindingAlreadyExists", "message": "Binding for port 710d70bd-597b-4f2c-8e71-796ebc36fead on host compute-1.redhat.local already exists.", "detail": ""}})