Revert default background policy

Policy was not working for guest user, resolved issue by providing image at build time

This reverts commit 13b4d4be.

app-misc/nayuos-chromium-policy/files/nayuos_policy.json

@@ -2,8 +2,4 @@
   "DefaultSearchProviderEnabled": true,
   "DefaultSearchProviderName": "DuckDuckGo",
   "DefaultSearchProviderSearchURL": "https://duckduckgo.com/?q={searchTerms}",
-  "WallpaperImage": {
-    "url": "https://softinst62285.host.vifib.net/public/Nayuos-Desktop.png",
-    "hash": "e070a65831492b2ba3415830690d14356ecdb7857ac0167e644129ff3312c16a"
-  }
 }