Remove DataSourceNone warning in cc_final_message

[TheRealFalcon]

Bug report

In the past, DataSourceNone was used purely as a fallback for when a primary datasource failed. However, DataSourceNone can be a datasource in an of itself and preferrable to NoCloud if all configuration is baked into the image. Because of this, it no longer makes sense to issue a warning in cc_final_message if None was expected. If there is defined userdata/metadata under the datasource definition in /etc/cloud or DataSourceNone is the only entry in the datasource_list, we should not warn that DataSourceNone was used.