elc_popup: Fix to make popup get proper size

elc_popup: Fix to make popup get proper size

Summary:
There is a bug that popup can't get proper size when list is set as its content.
Because of unneccesary calling evas_object_show() in popup's overriding elm_obj_container_content_set(),
sizing eval doens't work correctly.
This patch fixes this bug.

Test Plan:
Execute 14th popup sample in "elementary_test popup".
(popup-center-title + list content + 1 button)
After applying this patch, popup shows correctly.

Reviewers: seoz, Hermet

Reviewed By: Hermet

Subscribers: Hermet, seoz

Differential Revision: https://phab.enlightenment.org/D2158