Btrfs: remove residual code in delayed inode async helper

Btrfs: remove residual code in delayed inode async helper

Before applying the patch
  commit de3cb945db4d8eb3b046dc7a5ea89a893372750c
  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>