archive.s.o: drop mention "as of 2015" for Debian origin

The archive.s.o homepage reads "source packages from the Debian distribution (as of August 2015, via the snapshot service)", which is obsolete as we are now tracking Debian daily.

It should read "source packages from the Debian distribution" and be moved up after GitHub in the origin list.

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Migrated from T1081 (view on Phabricator)