xprtrdma: Update obsolete comment

Comment was made obsolete by commit 8cec3dba ("xprtrdma:
rpcrdma_regbuf alignment").
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/xprt_rdma.h

@@ -117,9 +117,6 @@ struct rpcrdma_ep {
 #endif
 
 /* Registered buffer -- registered kmalloc'd memory for RDMA SEND/RECV
- *
- * The below structure appears at the front of a large region of kmalloc'd
- * memory, which always starts on a good alignment boundary.
  */
 
 struct rpcrdma_regbuf {