Revert "mm: add free_hot_cold_page_list() helper"

This reverts commit 40c8351fc47204a33476a3cebb72b40fa677c51f.
Revert "memcg: clear pc->mem_cgroup if necessary."

This reverts commit 2f35eb2e69baeea89e43cd477c2a201572183cea.
Revert "Updated to latest Google Csnappy compressor for ZRAM."

This reverts commit 8029bd03f89a94a923963515056332c6498db707.