Hide the browser's native radio button on the custom background position selector in the Customizer and the legacy background screen. This fixes an issue causing both to display.
Props mukesh27, ravipatel, sabernhardt, walbo.
Fixes#53803.
Built from https://develop.svn.wordpress.org/trunk@51637
git-svn-id: http://core.svn.wordpress.org/trunk@51243 1a063a9b-81f0-0310-95a4-ce76da25c4cd