sst_importer may leak sst files once lightning encounters error due to wrong range loaded

[YuJuncen]

Bug Report

What version of TiKV are you using?

the current master

What operating system and CPU are you using?

unrelated

Steps to reproduce

Run tidb-lightning and make some region epoch changes between writing and ingesting.
More detailed:

1. Upload a SST by write.
2. But, don't ingest it.
3. Scatter the region bound to the SST meta, make the store we are writeing to no more has a peer of that region.

What did you expect?

After tidb-lightning exits, the SST file should be cleaned.

What did happened?

Even time passed 5 days, the SST file hasn't been removed.

[YuJuncen]

(Let's add the affects-* tags for 6.x firstly, I think this issue probably exists in the 5.x(even 4.x) versions. But it seems we haven't release patches over 5.x versions for a long time. So I guess it would be better to cherry-pick them when we are going to release new patch version?)