[tex-live] Cleaning backups doesn't work anymore

[Uwe Siart]

After today's update tlmgr fails to clean updates. Here's what I get on
a Win7 machine:

,----
| C:\>tlmgr backup newtx
| saving current status of newtx to C:/Programme1/texlive/2018/tlpkg/backups/newtx.r47889.tar.lz4
| 
| C:\>tlmgr backup --clean=0 --all
| 
| C:\>
`----

After this the backup file newtx.r47889.tar.lz4 is still there.

-- 
Uwe