func (s *Schema) Trim(version int) []Update {
	trimmed := s.updates[version:]
	s.updates = s.updates[:version]
	s.fresh = ""
	return trimmed
}
func (s *Schema) Trim(version int) []Update {
	trimmed := s.updates[version:]
	s.updates = s.updates[:version]
	s.fresh = ""
	return trimmed
}
// Trim the schema updates to the given version (included). Updates with higher
// versions will be discarded. Any fresh schema dump previously set will be
// unset, since it's assumed to no longer be applicable. Return all updates
// that have been trimmed.