[Matrix]: remove virtual methods in dense_matrix.
[Matrix]: remove virtual methods in dense_matrix.

zheng-da/FlashX,icoming/FlashX,icoming/FlashGraph,icoming/FlashGraph,zheng-da/FlashX,icoming/FlashX,icoming/FlashX,flashxio/FlashX,zheng-da/FlashX,icoming/FlashX,flashxio/FlashX,icoming/FlashX,icoming/FlashGraph,flashxio/FlashX,icoming/FlashGraph,flashxio/FlashX,flashxio/FlashX,zheng-da/FlashX,icoming/FlashGraph,zheng-da/FlashX,flashxio/FlashX