SUNRPC: Remove dprintk() in svc_handle_xprt()

When enabled, this dprintk() fires for every incoming RPC, which is
an enormous amount of log traffic. These days, after the first few
hundred log messages, the system journald is just going to mute it,
along with all other NFSD debug output.

Let's rely on trace points for this high-traffic information
instead.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>