multibuttonentry: fix MBE item clear, item delete logic error.

multibuttonentry: fix MBE item clear, item delete logic error.

Summary:
elm_multibuttonentry_clear API not worked well.
It deleted only odd items. Because of the sd->items has been modified inside elm_widget_item_del().

Then we don't have to search target item inside of _item_del().

@fix

Test Plan:
Add MBE items.
Call elm_multibuttonentry_clear API.
Check the bug state.

Reviewers: Hermet, cedric

Reviewed By: cedric

Differential Revision: https://phab.enlightenment.org/D3065

Signed-off-by: Cedric BAIL <cedric@osg.samsung.com>