LU-10994 clio: remove cpo_assume, cpo_unassume, cpo_fini

LU-10994 clio: remove cpo_assume, cpo_unassume, cpo_fini

Remove the cl_page methods cpo_assume, cpo_unassume, and
cpo_fini. These methods were only implemented by the vvp layer and so
they can be easily inlined into cl_page_assume() and
cl_page_unassume(). Remove vvp_page_delete() by inlining its contents
to cl_page_delete0().

Change-Id: I260c5593983bac6742cf7577c26a4903e95ceb7c
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/47373
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>