Revert "Skip test_remove_column_with_array_as_an_argument_is_deprecated ...

This reverts commit 7544c7a9f290a3ea25099ae38d52795458391785 made #6593

This pull request reverts "Skip test_remove_column_with_array_as_an_argument_is_deprecated with Oracle adapter." because Oracle enhanced adapter is supporting remove_column with Array. 

When this pull request merged, it should work as follows.

```ruby
$ ARCONN=oracle ruby -Itest test/cases/migration_test.rb -n test_remove_column_with_array_as_an_argument_is_deprecated
Using oracle with Identity Map off
Run options: -n test_remove_column_with_array_as_an_argument_is_deprecated

# Running tests:

.

Finished tests in 0.191176s, 5.2308 tests/s, 10.4615 assertions/s.

1 tests, 2 assertions, 0 failures, 0 errors, 0 skips
$
```