vdk-oracle: remove secrets config in favour of secrets overrides from vdk-core

[DeltaMichael]

Follow-up from https://github.com/vmware/versatile-data-kit/issues/1722

Overview

We should remove https://github.com/vmware/versatile-data-kit/blob/main/projects/vdk-plugins/vdk-oracle/src/vdk/plugin/oracle/oracle_plugin.py#L39 because it will be pulled from secrets anyway after #1722 is implemented.

Acceptance criteria

1. Remove the secrets override in vdk-oracle and rely on secrets fetched by vdk-core