bcache: Revert "bcache: shrink btree node cache after bch_btree_check()"

bcache: Revert "bcache: shrink btree node cache after bch_btree_check()"

This reverts commit 1683ab0ede4d0646fb1e09edf3d9a8b6333749e4.

In my testing, sometimes even all the cached btree nodes are freed,
creating gc and allocator kernel threads may still fail. Finally it
turns out that kthread_run() may fail if there is pending signal for
current task. And the pending signal is sent from OOM killer which
is triggered by memory consuption in bch_btree_check().

Therefore explicitly shrinking bcache btree node here does not help,
and after the shrinker callback is improved, as well as pending signals
are ignored before creating kernel threads, now such operation is
unncessary anymore.

This patch reverts the commit 1683ab0ede4d ("bcache: shrink btree node
cache after bch_btree_check()") because we have better improvement now.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>