Revert "staging: zcache: fix cleancache race condition with shrinker"

This reverts commit a7ec9f7b2a08f92dc48e18665758e7f30f48abed.
Revert "staging: fix zcache building"

This reverts commit 45c61d60e83455aa514df12298ecb32a60896ec4.
zcache cleanup