[multi-sources] closes #1918120: drop behaviour leading to wrong result as demonstrated by the ticket The formerly implemented behaviour doesn't seems to be useful, nor to have a chance to be correct. At least no test case demonstrate the opposite, so I've dropped it.

if repo.system_source.dbdriver == 'postgres':
    sql('ALTER TABLE appears ADD COLUMN weight float')
    sql('UPDATE appears SET weight=1.0 ')