chore: simplify delete namespace sql query

iox_catalog/src/postgres.rs

@@ -684,15 +684,8 @@ WHERE name = $1;
         // note that there is a uniqueness constraint on the name column in the DB
         sqlx::query(
             r#"
-WITH namespace_id as (
-    SELECT id
-    FROM namespace
-    WHERE name = $1
-    LIMIT 1
-)
 DELETE FROM namespace
-WHERE id = (SELECT id FROM namespace_id)
-RETURNING id;
+WHERE name = $1;
         "#,
         )
         .bind(name)