Oracle database can run `delete` statement with `order by` and`fetch first n rows only`

Since https://github.com/rails/arel/pull/337 Oracle adapter uses better
top N query using `fetch first n rows only`, which can remove this
unless condition.

* This commit passes with Oracle database
```ruby
$ ARCONN=oracle bin/test test/cases/relation/delete_all_test.rb -n test_delete_all_with_order_and_limit_deletes_subset_only
Using oracle
Run options: -n test_delete_all_with_order_and_limit_deletes_subset_only --seed 1081

.

Finished in 8.068626s, 0.1239 runs/s, 0.6197 assertions/s.
1 runs, 5 assertions, 0 failures, 0 errors, 0 skips
$
```

* SQL statement includes `ORDER BY` and `FETCH FIRST n ROWS ONLY`

```sql
  Post Destroy (12.5ms)  DELETE FROM "POSTS" WHERE "POSTS"."ID" IN (SELECT "POSTS"."ID" FROM "POSTS" WHERE "POSTS"."AUTHOR_ID" = :a1 ORDER BY "POSTS"."ID" ASC FETCH FIRST :a2 ROWS ONLY)  [["author_id", 1], ["LIMIT", 1]]
```

0 files changed, 0 insertions, 0 deletions