sql/schemachanger: fix incorrect clean up of sequnece ownership

Previously, when a default expression was cleaned up the sequence
ownerships would be incorrectly cleaned up. This meant when we added
support for setting default expressions in the declarative schema
changer, any updates could wipe out sequence ownership information. To
address this, this patch removes the incorrect clean up logic.

Fixes: #151925

Release note (bug fix): Updating column default expressions would
incorrectly remove sequence ownerships for the affected column.

Author: fqazi

pkg/sql/logictest/testdata/logic_test/sequences

@@ -2536,3 +2536,25 @@ SELECT substring(sequence_schema FOR 7), sequence_name FROM [SHOW SEQUENCES] WHE
 pg_temp  temp_seq
 
 subtest end
+
+
+subtest incorrect_cleanup_of_owned_by
+
+statement ok
+CREATE TABLE t_seq_owner (id BIGSERIAL NOT NULL);
+
+statement ok
+CREATE SEQUENCE id_seq_owned OWNED BY t_seq_owner.id;
+
+statement ok
+ALTER TABLE t_seq_owner ALTER COLUMN id SET DEFAULT nextval('id_seq_owned');
+
+statement ok
+drop table t_seq_owner;
+
+query I
+SELECT count(*) FROM [SHOW TABLES] WHERE table_name='id_seq_owned'
+----
+0
+
+subtest end

pkg/sql/schemachanger/scexec/scmutationexec/helpers.go

@@ -280,7 +280,6 @@ func updateColumnExprSequenceUsage(d *descpb.ColumnDescriptor) error {
 		ids.ForEach(all.Add)
 	}
 	d.UsesSequenceIds = all.Ordered()
-	d.OwnsSequenceIds = all.Ordered()
 	return nil
 }