libcephfs_proxy: remove unnecessary protocol references in client

With the new protocol structure definitions, it's not necessary to
explicitly access each field inside its version substructure (v0, for
example). Now all fields of the latest version are declared inside an
anonymous substructure that can be accessed without a prefix.

Fixes: https://tracker.ceph.com/issues/72800
Signed-off-by: Xavi Hernandez <[email protected]>

Author: xhernandez