Revert 274198 "Depend on v8:v8 instead of v8:mksnapshot"

> Depend on v8:v8 instead of v8:mksnapshot
> 
> BUG=none
> R=brettw@chromium.org
> 
> Review URL: https://codereview.chromium.org/302783009

TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/308303003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274201 0039d316-1c4b-4281-b951-d872f2087c98

BUILD.gn

@@ -85,7 +85,7 @@ group("root") {
     "//ui/strings",
     "//ui/surface",
     "//url",
-    "//v8:v8",
+    "//v8:mksnapshot",
     "//webkit/browser:storage",
     "//webkit/child",
   ]