LU-10994 clio: remove cpo_prep and cpo_make_ready

LU-10994 clio: remove cpo_prep and cpo_make_ready

Remove the cpo_prep and cpo_make_ready methods from struct
cl_page_operations. These methods were only implemented by the vvp
layer and so they can be easily inlined into cl_page_prep() and
cl_page_make_ready().

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I177fd8d3c3832bcc8f06ed98cdf9d30f18d49e88
Reviewed-on: https://review.whamcloud.com/47399
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>