IB/usnic: Remove stub functions

Lack of mandatory verbs no longer fail device registration, the device
will be marked as a non-kverbs provider.

Signed-off-by: Gal Pressman <galpress@amazon.com>
Tested-by: Parvi Kaustubhi <pkaustub@cisco.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>