Remove old mobile theme background color

It's enough to just fall back on the default background color.

index.html

@@ -5,7 +5,6 @@
     <meta name="viewport" content="width=device-width, initial-scale=1" />
     <meta name="name" content="Radicle Interface" />
     <meta name="description" content="Interact with Radicle" />
-    <meta name="theme-color" content="#0e171f" />
     <meta property="og:title" content="Radicle Interface" />
     <meta property="og:description" content="Interact with Radicle." />
     <meta property="og:url" content="https://app.radicle.xyz" />

public/app.webmanifest

@@ -4,7 +4,6 @@
   "short_name": "Radicle",
   "description": "Interact with Radicle.",
   "start_url": "/",
-  "theme_color": "#0e171f",
   "icons": [
     {
       "src": "/images/apple-touch-icon.png",