Remove WP_Cache non_existant_objects array
|Reported by:||duck_||Owned by:||duck_|
|Component:||Cache API||Keywords:||has-patch needs-testing dev-feedback|
This was introduced back in  "for options, which has its own notoptions cache these days" (ryan), to help reduce file system hits.
Right now it appears to just take up a bit of extra memory and cause incorrect figures on cache misses (assuming that we do want to report a 2nd request for an uncached item as a miss).
Noticed this as a result of investigation prior to #15812, I saw that stats was showing no increase in cache misses and I thought this a little strange but didn't question it too much.