Remove the configuration options for sync integrations

When you install this module, you are presented with confusing options on "Account integration", which a Drupal user such as myself would think meant "Drupal account integration". You can see that other users have this expectation too, as demonstrated in #1256948: Create drupal account on new subscription?.

So in order to avoid confusion *and* to make it so that we have more consistently available features within the module and less special casing, let's just remove the option entirely and always turn on recording of local Recurly account information.

So far I haven't found an actual purpose for this functionality though, so perhaps we can remove it entirely in the future. For now let's leave it intact because I can imagine some usefulness of this data (Views integration for example), but considering the point of Recurly module is to offload the responsibility of the Drupal site as much as possible, data synchronization seems like an unnecessary effort.