Btrfs: remove residual code in delayed inode async helper

Btrfs: remove residual code in delayed inode async helper

Before applying the patch
  commit d2d3a46d646d7c63e6b07dc58318c7c90b64d0f9
  title: Btrfs: improve the delayed inode throttling

We need requeue the async work after the current work was done, it
introduced a deadlock problem. So we wrote the code that this patch
removes to avoid the above problem. But after applying the above
patch, the deadlock problem didn't exist. So we should remove that
fix code.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>