vpn-manager: Migrate libchromeos to its own ebuild

All platform2 packages should have their own ebuild that will be compiled
independently. Packages should DEPEND on libchromeos and should not have a gyp
dependency on libchromeos's gyp file anymore.

BUG=chromium:381372
TEST=emerge-daisy libchromeos && emerge-daisy platform2 work
TEST=trybot run on daisy, link, mario and duck.
TEST=trybot run on lumpy-incremental-paladin.

CQ-DEPEND=CL:202748

Change-Id: I061d55a941fbd7210b0bbf65daa07c9ae2198bc6
Reviewed-on: https://chromium-review.googlesource.com/202764
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Bertrand Simonnet <bsimonnet@chromium.org>
diff --git a/vpn-manager.gyp b/vpn-manager.gyp
index b4a4f4f..231969b 100644
--- a/vpn-manager.gyp
+++ b/vpn-manager.gyp
@@ -1,11 +1,9 @@
 {
   'target_defaults': {
-    'dependencies': [
-      '../../platform2/libchromeos/libchromeos-<(libbase_ver).gyp:libchromeos-<(libbase_ver)',
-    ],
     'variables': {
       'deps': [
         'libchrome-<(libbase_ver)',
+        'libchromeos-<(libbase_ver)',
         'openssl',
       ],
     },