Subscriptions block: Remove option to place button on new line when using compact style

### Impacted plugin

Jetpack

### Issue

After adding a Subscriptions block in the editor and selecting 'Compact' under the Styles, there is still an option to place the button on a new line under 'Settings' in the sidebar. This has exactly the same effect as choosing 'Split' instead of 'Compact', so seems redundant and confusing.

Could that option be removed when 'Compact' is selected?

Mentioned in internal testing: p8oabR-11U-p2#comment-6963

Start in the Jetpack Subscriptions block's editor Styles and sidebar Settings controls, comparing the Compact and Split options described in the issue. Verify the sidebar no longer offers the new-line button option for Compact, while the equivalent Split behavior remains available, then confirm the block still renders correctly in the editor.

Written by the indexing model from the issue text.