styles: use flat color for background (removes noise.png)

Personally I think it looks better with a flat green color instead of
the `noise.png` image overlay.

Author: tarcieri

app/styles/application.module.css

@@ -14,7 +14,6 @@
 }
 
 html {
-    background: url('/assets/noise.png');
     background-color: #3b6837;
 }