LU-13814 osc: Remove osc delete for transient pages

LU-13814 osc: Remove osc delete for transient pages

Transient pages do not need an extra reference for being
part of a transfer, because they are referenced throughout
by cl_io.  This requires a tweak to the page completion
behavior.

This allows us to remove osc_page_delete for transient
pages.

Signed-off-by: Patrick Farrell <patrick.farrell@oracle.com>
Change-Id: I96539731f972b19830b2e08bf0f1d1f1e9674241
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52079
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>