remove archive/17.0.0-200/MOSDScrub

remove archive/17.0.0-200/MOSDScrub

since we don't have any corpus for MOSDScrub, there is no need
to create this file. also we should create the file named $type under
"forward_incompat". so, if we have had some corpus for MOSDScrub,
we could create a file at

archive/15.2.1-40-ga838bb1aae/objects/MOSDScrub

assuming the corpus of MOSDScrub is located under
archive/15.2.1-40-ga838bb1aae/objects.

this change is a follow-up of 20e09990f9faf8998da8d2ee403393043be6405d

Signed-off-by: Kefu Chai <tchaikov@gmail.com>