code: def downgrade():
      with op.batch_alter_table("slices") as batch_op:
          batch_op.drop_constraint(
              "slices_last_saved_by_fk", type_="foreignkey"
          )
          batch_op.drop_column("last_saved_by_fk")
          batch_op.drop_column("last_saved_at")
  
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