Remove a bunch of broken/unused/non-useful NTP UMA histograms

chrome/browser/resources/local_ntp/most_visited_util.js

Index: chrome/browser/resources/local_ntp/most_visited_util.js
diff --git a/chrome/browser/resources/local_ntp/most_visited_util.js b/chrome/browser/resources/local_ntp/most_visited_util.js
index 7c10a59f5ce11d65dc0117ca7c8b258b7b64a29b..ded836eb7806e2fd1376c608a1bcecbdf3e6aaea 100644
--- a/chrome/browser/resources/local_ntp/most_visited_util.js
+++ b/chrome/browser/resources/local_ntp/most_visited_util.js
@@ -30,20 +30,6 @@ var NTP_LOGGING_EVENT_TYPE = {
   // Indicates a tile was rendered, no matter if it's a thumbnail, a gray tile
   // or an external tile.
   NTP_TILE: 2,
-  // The tile uses a local thumbnail image.
-  NTP_THUMBNAIL_TILE: 3,
-  // Used when no thumbnail is specified and a gray tile with the domain is used
-  // as the main tile.
-  NTP_GRAY_TILE: 4,
-  // The visuals of that tile are handled externally by the page itself.
-  NTP_EXTERNAL_TILE: 5,
-  // There was an error in loading both the thumbnail image and the fallback
-  // (if it was provided), resulting in a grey tile.
-  NTP_THUMBNAIL_ERROR: 6,
-  // Used a gray tile with the domain as the fallback for a failed thumbnail.
-  NTP_GRAY_TILE_FALLBACK: 7,
-  // The visuals of that tile's fallback are handled externally.
-  NTP_EXTERNAL_TILE_FALLBACK: 8,
   // A NTP Tile has finished loading (successfully or failing).
   NTP_TILE_LOADED: 10,
 };