packaging: setup: reinstate clear database

commit 1156dad0 introduced cleandb at dbscripts, however when we
upgrade, dbscript may be rolled back before we rollback the database.

this change is partial rollback, with the addition of adding the
function drop syntax generation, so even in minimal database we will be
able to reproduce this syntax.

Change-Id: I14ac6a43ac4d5510c2664e82283ae03cd22456ba
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>