nfs: Don't generate duplicated events

The events are already generated by vfs_readv and vfs_writev.
splice does not seem to generate the events, but that's an
other bug.

The patch also removes a couple of unneeded fsnotify.h
inclusions from fs/cachefiles/.

Signed-off-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Signed-off-by: Eric Paris <eparis@redhat.com>