LU-2335 build: stop checking for XATTR_ACL_SIZE

LU-2335 build: stop checking for XATTR_ACL_SIZE

posix_acl_xattr_size() never changed in all kernels, liblustre
also implements the same as in kernel.
So XATTR_ACL_SIZE can be calculated at compile time and doesn't
need to be checked.

Removing it can reduce parameters that need to exist in Kconfig.

Signed-off-by: Peng Tao <tao.peng@emc.com>
Change-Id: I64584f04055b06f26e1c08f834d4683f97841332
Reviewed-on: http://review.whamcloud.com/4644
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>