Update gyp files to depend on metrics' standalone ebuild.

Metrics is now installed by chromeos-base/metrics.
Platform2 packages should depend on it through the variable:deps mechanism
instead of depending directly on metrics' gyp file.

BUG=chromium:387923
TEST=Build platform2. metrics gets installed and the tests succeed.
TEST=Trybot run on daisy-release, lumpy-incremental-paladin, link-release,
  duck-release, x86-mario-release.

CQ-DEPEND=CL:205312

Change-Id: Id6fbb81234d9f874e034afcb3df16069608f32e7
Reviewed-on: https://chromium-review.googlesource.com/205321
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>

buffet/buffet.gyp

diff --git a/buffet/buffet.gyp b/buffet/buffet.gyp
index 8f7ba6e..17a85bc 100644
--- a/buffet/buffet.gyp
+++ b/buffet/buffet.gyp
@@ -1,14 +1,12 @@
 {
   'target_defaults': {
-    'dependencies': [
-      '<(platform_root)/metrics/libmetrics-<(libbase_ver).gyp:libmetrics-<(libbase_ver)',
-    ],
     'variables': {
       'deps': [
         'dbus-1',
         'libchrome-<(libbase_ver)',
         'libchrome-test-<(libbase_ver)',
         'libcurl',
+        'libmetrics-<(libbase_ver)',
       ],
     },
     'link_settings': {