sql: sequence owner's ColumnDescriptor not updated after owned sequence is dropped

[RichardJCai]

Repro, have to inspect ColumnDescriptor of the column that owns the seq after the drop seq as no query shows this.

CREATE TABLE t(x INT);
CREATE SEQUENCE seq OWNED BY t.x;
DROP SEQUENCE seq;

# Need to manually inspect ColumnDescriptor for t.x after, one way is to drop the column and print the descriptor's OwnedSequenceIDs. The list will still contain the seq's ID.

[RichardJCai]

Closing since #50649 encapsulates this issue.