LU-812 synchronize_rcu no longer a define

LU-812 synchronize_rcu no longer a define

synchronize_kernel() in old kernel(pre 2.6.12) is no longer supported
and synchronize_rcu is no longer a define after 2.6.33. Remove the no
longer used old code.

Change-Id: Iac668efc35d82e6218b1924eca009f92d19a0c7a
Signed-off-by: Wally Wang <wang@cray.com>
Reviewed-on: http://review.whamcloud.com/1952
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>