nfs: no PG_private waiters remain, remove waker

nfs: no PG_private waiters remain, remove waker

Since commit 4f52b6bb8c57 ("NFS: Don't call COMMIT in ->releasepage()"),
no tasks wait on PagePrivate.

Thus the wake introduced in commit 9590544694be ("NFS: avoid deadlocks
with loop-back mounted NFS filesystems.") can be removed.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Nicholas Piggin <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: Anna Schumaker <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>