Remove v8 gn config from secondary tree

We'll important the BUILD.gn into v8 instead to make maintaining it
easier

BUG=none
R=brettw@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/253843008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@268170 0039d316-1c4b-4281-b951-d872f2087c98

BUILD.gn

@@ -56,7 +56,6 @@ group("root") {
     "//ui/gfx",
     "//ui/resources",
     "//url",
-    "//v8:v8_base",
   ]
 
   if (is_linux) {