LU-15619 osc: Remove oap_magic

LU-15619 osc: Remove oap_magic

oap_magic exists only to debug init and allocation
failures, but is allocated for every page of memory, which
wastes a lot of memory for something we don't need
dedicated debug for.

Remove it.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I360e09676f7ba8c3e5296bdf75a6e7f75e91eadb
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/46713
Reviewed-by: Zhenyu Xu <bobijam@hotmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>