SUNRPC: Remove CONFIG_SUNRPC_REGISTER_V4

We just augmented the kernel's RPC service registration code so that
it automatically adjusts to what is supported in user space.  Thus we
no longer need the kernel configuration option to enable registering
RPC services with v4 -- it's all done automatically.

This patch is part of a series that addresses
   http://bugzilla.kernel.org/show_bug.cgi?id=12256

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>