This improves UX, since an image added will be displayed on front end as opposed to not at all. This fix added the front page's featured image above the front page content, similar to how it's handled in the other panels. Also it removed code that was setting the front page's featured image as a fallback to the custom header, and updated the conditions that add the `has-header-image` to remove reference to the front page's featured image.
Props laurelfulford.
Fixes#38402.
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git-svn-id: http://core.svn.wordpress.org/trunk@38811 1a063a9b-81f0-0310-95a4-ce76da25c4cd