Widgets: Subscription widget is still active after deactivating widgets

I'm aware that this widget is still visible because you have to deactivate the Subscriptions feature. However, that might not be clear to our users. I'm logging this here since we might want to revisit this behavior.

#### Steps to reproduce the issue

1. Go to `jetpack_modules` and deactivate Extra Sidebar Widgets
2. Go to Appearance > Widgets
3. The subscriptions widget is still visible

#### What I expected
I didn't expect the subscriptions widget to be visible

#### What happened instead
The widget was still visible

**Screenshots**

### When Extra Sidebar Widgets is active

### When Extra Sidebar Widgets is inactive

Reproduce the issue by deactivating Extra Sidebar Widgets in jetpack_modules, then checking Appearance > Widgets. Trace how the subscriptions widget remains registered after that module is disabled. Done means the intended widget visibility behavior is established and verified against the reproduction steps.

Written by the indexing model from the issue text.