download.pl: properly cleanup intermediate .hash file
It seems like after a build the /dl dir seems to now contain a .hash
file for each source file due to inproper cleanup so fix it by removing
those intermediate files before leaving the download action.
Fixes: 4e19cbc55335 ("download: handle possibly invalid local tarballs")
Reported-by: Hannu Nyman <[email protected]>
Signed-off-by: Petr Štetiar <[email protected]>