LU-10994 clio: remove struct vvp_page

LU-10994 clio: remove struct vvp_page

Remove struct vvp_page and use struct cl_page_slice in its place. Use
cp_vmpage in place of vpg_page and cl_page_index() in place of
vvp_index().

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I2cd408f08e6ff9f7686b591c02ea95e31ad2b2ae
Reviewed-on: https://review.whamcloud.com/47400
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>