NFS do not clear minor version at nfs_client free

Resetting the client minor version operations causes nfs4_destroy_callback
to fail to shutdown the NFSv4.1 callback service.

There is no reason to reset the client minorversion operations when the
nfs_client struct is being freed.

Remove the minorverion reset and rename the function.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>