Bug 32284: Remove checked binary after check

When checking our .mar and .exe files for signing errors we keep the
checked files around until the whole check is done. This essentially
leads to doubling the amount of disk space for them during that time,
which could make the difference between someone being able to check
them successfully or not.

There is actually no need, though, to keep all the binaries until the
whole signature check is done and we remove the checked bundle from now
on immediately after a particular check finished.