The 7000 scientific delegates who will attend the weeklong Bio2000 Conference on genetically engineered foods in Boston starting March 25, are bracing for a week of counter-demonstrations by a coalition of protest groups calling themselves Biodevastation 2000. The Boston police predict peaceful protests — unlike Seattle — but have taken the high-security step of removing vending and newspaper boxes from heavily traveling downtown streets. “We’ve never done this for any other convention,” a frustrated newspaper circulation manager said.