Revert "mm: methods for teaching filesystems about PG_swapcache pages"

This reverts commit 2f002afacd56924c975b2e6ad2df89eab5976c25.
look for zsmalloc.h under include/linux
Revert "mm: frontswap/cleancache: final flush->invalidate"

This reverts commit ddbd22f4d3701dfaf499e07f3bea63af490d0b46.