Btrfs: Don't wait on tree block writeback before freeing them anymore

This isn't required anymore because we don't reallocate blocks that
have already been written in this transaction.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --cc fs/btrfs/ctree.c
Simple merge

diff --cc fs/btrfs/extent-tree.c
Simple merge

diff --cc fs/btrfs/inode.c
Simple merge