Revert "Use SimpleEntry in StorageMap." This reverts commit fc3088d7b42e123df81de2879f8a6c7d0a2ba12e. Breaks build. See: http://build.gwtproject.org/job/gwt/168/testReport/com.google.gwt.storage.client/LocalStorageMapTest/ Change-Id: I668d8643eb700690c31907f72aae0c1172bc26f9