[dataset] remove unused method declaration in DatasetLocal (#2495)

src/core/meshcop/dataset_local.hpp

@@ -136,15 +136,6 @@ public:
      */
     otError Set(const Dataset &aDataset);
 
-    /**
-     * This method restores dataset from non-volatile memory.
-     *
-     * @retval OT_ERROR_NONE       Successfully restore the dataset.
-     * @retval OT_ERROR_NOT_FOUND  There is no corresponding dataset stored in non-volatile memory.
-     *
-     */
-    otError Restore(void);
-
     /**
      * This method compares this dataset to another based on the timestamp.
      *