#5067016 Premium Content: Remove double banners

Changes proposed in this Pull Request

Update the premium content block to remove the Stripe connect banner, and the subscriber/non subscriber banner. Doing this means there is no persistent block UI in the canvas, improving the design experience for patterns using this block. These two banners have been merged into the block toolbar for the block.

Before	After
Multiple “banners” when selecting the block.	Options from the old banners merged into the block toolbar.

Testing instructions

• Check out this branch locally and run yarn dev --sync in the wp-calypso/apps/editing-toolkit directory
• Open up a site on your sandbox and insert the premium content block.
• Confirm that you see the “After” UI above.
• Confirm that you can connect stripe and the “Connect Stripe” button disappears.
• Confirm that you can switch back and forth between the Visitor, and Subscriber views.
• Confirm that you can edit blocks in both views.

Fixes Automattic/view-design#84
cc @ianstewart