Remove current_adapter? from test_sanitize_sql_hash_handles_associations

This pull request addresses the following Failure since 0f97ac66471270b917103869a56bc409aa3ccf0b merged to master.

```ruby
$ ARCONN=oracle ruby -Itest test/cases/sanitize_test.rb -n test_sanitize_sql_hash_handles_associations
Using oracle
Run options: -n test_sanitize_sql_hash_handles_associations --seed 34232

# Running tests:

F

Finished tests in 0.015117s, 66.1522 tests/s, 66.1522 assertions/s.

  1) Failure:
SanitizeTest#test_sanitize_sql_hash_handles_associations [test/cases/sanitize_test.rb:15]:
--- expected
+++ actual
@@ -1 +1 @@
-"\"adorable_animals\".\"name\" = 'Bambi'"
+"\"ADORABLE_ANIMALS\".\"NAME\" = 'Bambi'"


1 tests, 1 assertions, 1 failures, 0 errors, 0 skips
$
```

This commit removes current_adapter by using ActiveRecord::ConnectionAdapters::Quoting methods.