NFSD: Minor cleanup in layoutcommit processing

Remove dprintk in nfsd4_layoutcommit. These are not needed
in day to day usage, and the information is also available
in Wireshark when capturing NFS traffic.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sergey Bashirov <sergeybashirov@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>