BACKPORT: dm bufio: remove old-style buffer cleanup

Remove code that cleans up buffers if the cache size grows over the limit.

The next commit will introduce a new global cleanup.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
(cherry picked from commit b132ff333201784e67654663360a1a4fb103ebe2)

Bug: 136247322
Change-Id: I6ceb363093cd2a73a51ca284630bd97466bc1be3
Signed-off-by: Martijn Coenen <maco@android.com>