LU-13814 osc: specialize osc_page_delete

LU-13814 osc: specialize osc_page_delete

Nearly all of osc_page_delete is only done for cacheable pages,
so make that explicit.  osc_lru_del() doesn't do anything because
transient pages can't go in the LRU.  In osc_teardown_async_page(),
the latter side of the if statement is a search in cache, so it
never finds the page, then the earlier part is a check that the
page isn't in an RPC.  That's not really possible for DIO pages
unless something is *really* off.

Signed-off-by: Patrick Farrell <patrick.farrell@oracle.com>
Change-Id: I998fc196c276aa97829f5b368e23aa4b7a797294
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52078
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>