Ensure expected notice is hidden when theme support enabled by theme

[westonruter]

Fixes #1358.

Before

When native support added by theme

add_theme_support('amp');

The notice appears but the checkbox should be hidden.

When paired support added by theme

add_theme_support( 'amp', array(
	'paired' => true,
) );

The checkbox appears but the notice should be hidden.

After

Native mode ✅

Paired mode ✅