script to nuke items from th-archive that are already in snap

script to nuke items from th-archive that are already in snap

objective for such cleanup is to decrease number of packages in th-archive:
1. faster loading of index
2. poldek hardcoded 64k limit of packages per repo

before:

source packages in th-archive: 20120

estimated[1] packages to remove:
2012: 3514 packages
2013: 3996 packages
2014: 4452 packages
2015: 3279 packages

after:

packages removed from th-archive that were present in snap:
2012: 3520 packages
2013: 2493 packages
2014: 2569 packages
2015: 2443 packages

source packages in th-archive: 9451

[1] does not account that package can be also in earlier snap