LU-10994 lov: remove lov_page

LU-10994 lov: remove lov_page

Remove the lov page layer since it does nothing but costs 24 bytes per
page plus pointer chases.

Lustre-change: https://review.whamcloud.com/47221
Lustre-commit: 56f520b1a4c9ae64caa235e9ce7699e7fb627f0c

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: Icd7b4b0041e0fe414a3a4143179f45845177960e
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/54033
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>