Remove NatGeo loading desktop story

Forgot to remove this story in https://chromium-review.googlesource.com/c/chromium/src/+/1101922

TBR=kouhei@chromium.org

Change-Id: I72b38dcbb165b29e446b75ba02351d5a1afcab69
Reviewed-on: https://chromium-review.googlesource.com/1103698Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#567886}

tools/perf/page_sets/loading_desktop.py

@@ -86,7 +86,6 @@ class LoadingDesktopStorySet(story.StorySet):
          ('http://www.imdb.com/title/tt0910970/', 'IMDB'),
          ('http://www.flickr.com/search/?q=monkeys&f=hp', 'Flickr'),
          ('http://money.cnn.com/', 'money.cnn'),
-         ('http://www.nationalgeographic.com/', 'NatGeo'),
          ('http://premierleague.com', 'PremierLeague'),
          ('http://walgreens.com', 'Walgreens'),
          ('http://colorado.edu', 'Colorado.edu'),