Update comment on feature_engagement

Mac now runs with Views. I couldn't think of a good reason to keep the
ChromeOS comment either, so I nuked it.

Change-Id: Ia49b6e5cce021996c495f121fc093cfd756ed56c
Reviewed-on: https://chromium-review.googlesource.com/c/1450018
Commit-Queue: Scott Violet <sky@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Auto-Submit: Scott Violet <sky@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628463}

components/feature_engagement/features.gni

@@ -4,7 +4,6 @@
 
 declare_args() {
   # In-Product Help is only available in Windows and Linux OS for
-  # desktop. Other platforms such as Mac OS currently does not support
-  # Views and there have been no strong feelings about CrOS.
+  # desktop.
   enable_desktop_in_product_help = is_win || (is_linux && !is_chromeos)
 }