Remove `domain` from floating-ip-dns-create-or-update-req body

`domain` is passed in the url req id, so it is unuseful in the
request body, remove it and v3 api-samples.

Change-Id: If8bdfb7fc928daaf01c9612c97c6b391d3139505
Merge "Remove `domain` from floating-ip-dns-create-or-update-req body"