Add forgotten cleanup of fairway dimensions This is actually a fixup of rev. e21cbb9768a2, that added database schema version 1431 with a constraint trigger preventing new or updated rows to have a duplicate area but missed to cleanup existing data. So cleanup now, before the duplicates hurt in future imports that try to keep the duplicates in history.

teichmann@intevation.de = sascha.teichmann@intevation.de
bernhard.reiter@intevation.de = bernhard@intevation.de