Remove src/platform/metrics from the manifest

metrics has been moved to platform2, we can remove it from the manifest now.

BUG=chromium:370259
TEST=None

Change-Id: Ie8d0647dc1f4578b51a2d8717ab2968bb95b292f
Reviewed-on: https://chromium-review.googlesource.com/205829

Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>

full.xml

@@ -86,7 +86,6 @@ Your sources have been sync'd successfully.
   <project path="src/platform/lorgnette" name="chromiumos/platform/lorgnette" />
   <project path="src/platform/memento_softwareupdate"
            name="chromiumos/platform/memento_softwareupdate" />
-  <project path="src/platform/metrics" name="chromiumos/platform/metrics" />
   <project path="src/platform/microbenchmark"
            name="chromiumos/platform/microbenchmark" />
   <project path="src/platform/minijail" name="chromiumos/platform/minijail" />