main/busybox: prevent warnings appearing during package upgrade
The busybox.post-upgrade script deletes softlinks for any busybox commands that have been removed between the previous busybox package version and this new version. However a side-effect is that for each new command added by the new version the terminal will show the following warnings/errors on stderr:
stat: can't stat 'usr/bin/last': No such file or directory
This MR ensures that these warning/errors do not appear.
Fixes #13321 (closed).