Remove platform-specific dead code for KeyedStores

R=jkummerow@chromium.org

Review URL: https://chromiumcodereview.appspot.com/22745003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16227 ce2b1a6d-e550-0410-aec6-3dcde31c8c00