Remove fixed min-height, let popup auto-size to content

Browser popups auto-size to fit content. A fixed min-height
forced the body taller than the browser allows, causing
scrollbars. Now each view is exactly as tall as it needs to be.

src/popup/styles/main.css

@@ -14,5 +14,4 @@
 
 body {
     width: 396px;
-    min-height: 720px;
 }