Revert "NFS: add nfs_sb_deactive_async to avoid deadlock"

This reverts commit 324d003b0cd82151adbaecefef57b73f7959a469.

The deadlock turned out to be caused by a workqueue limitation that has
now been worked around in the RPC code (see comment in rpc_free_task).

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --cc fs/nfs/inode.c
Simple merge

diff --cc fs/nfs/internal.h
Simple merge

diff --cc fs/nfs/nfs4proc.c
Simple merge

diff --cc fs/nfs/super.c
Simple merge

diff --cc fs/nfs/unlink.c
Simple merge