code: def downgrade():
      op.drop_column("dbs", "force_ctas_schema")
      op.drop_column("dbs", "expose_in_sqllab")
      op.drop_column("dbs", "allow_ctas")
  
imports: import sqlalchemy
  from alembic import op
label_desc: Use image node_id 2 for calling a global function with example usage: downgrade() without return types