Use new dark mode icon as built-in feed icon.

iOS/Resources/Assets.xcassets/nnwFeedIcon.imageset/Contents.json

@@ -1,17 +1,15 @@
 {
   "images" : [
     {
-      "filename" : "feedIcon.png",
+      "filename" : "Dark Icon.png",
       "idiom" : "universal",
       "scale" : "1x"
     },
     {
-      "filename" : "feedIcon 1.png",
       "idiom" : "universal",
       "scale" : "2x"
     },
     {
-      "filename" : "feedIcon 2.png",
       "idiom" : "universal",
       "scale" : "3x"
     }