xprtrdma: Remove rpcrdma_create_data_internal::rsize and wsize

Clean up.

xprt_rdma_max_inline_{read,write} cannot be set to large values
by virtue of proc_dointvec_minmax. The current maximum is
RPCRDMA_MAX_INLINE, which is much smaller than RPCRDMA_MAX_SEGS *
PAGE_SIZE.

The .rsize and .wsize fields are otherwise unused in the current
code base, and thus can be removed.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>