Left overs from uploads of the same package version but different distribution

Reported by @bartm,

When a package is uploaded for the same version but with a different distribution, on package cleanup, debexpo will only remove entries from the official upload distribution.

To mitigate this issue, we can either:

Reject uploads for the same version with a different distribution
Remove all versions of a package regardless of its distribution upon official upload

@mattia, what do you think of that?

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