bcache: Kill unused freelist

This was originally added as at optimization that for various reasons isn't
needed anymore, but it does add a lot of nasty corner cases (and it was
responsible for some recently fixed bugs). Just get rid of it now.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

diff --cc drivers/md/bcache/alloc.c
Simple merge

diff --cc drivers/md/bcache/bcache.h
Simple merge

diff --cc drivers/md/bcache/btree.c
Simple merge

diff --cc drivers/md/bcache/btree.h
Simple merge

diff --cc drivers/md/bcache/super.c
Simple merge

diff --cc include/trace/events/bcache.h
Simple merge