* wl-summary.el (wl-summary-set-message-modified): No use

* wl-summary.el (wl-summary-set-message-modified): No use
elmo-folder-set-message-modified and wl-summary-set-mark-modified.
(wl-summary-set-mark-modified): Abolish.
(wl-summary-mark-modified-p): Ditto.
(wl-summary-save-view): Follow the change above.

* wl-expire.el (wl-summary-expire): Likewise.

* elmo.el (luna-define-class): Remove slot message-modified and
flag-modified.
(elmo-folder-set-message-modified): Abolish.
(elmo-generic-folder-commit): Follow the change above.
(elmo-folder-synchronize): Ditto.

* elmo-pipe.el (elmo-folder-set-message-modified): Abolish.

* elmo-multi.el (elmo-folder-set-message-modified): Ditto.

* elmo-filter.el (elmo-folder-set-message-modified): Ditto.