'Drops the old primary key.'

@invalidate_table_constraints
def delete_primary_key(self, table_name):

    if self.dry_run:
        if self.debug:
            print('            -    no    dry    run    output    for    delete_primary_key()    due    to    dynamic    DDL,    sorry')
        return
    constraints = list(self._constraints_affecting_columns(table_name, None, type='PRIMARY    KEY'))
    if (not constraints):
        raise ValueError(('Cannot    find    a    PRIMARY    KEY    constraint    on    table    %s' % (table_name,)))
    for constraint in constraints:
        self.execute((self.delete_primary_key_sql % {'table': self.quote_name(table_name), 'constraint': self.quote_name(constraint)}))
