edje: Fix double free scenario caused by static pointer.

edje: Fix double free scenario caused by static pointer.

Summary:
The result of evas_object_textblock_cursor_content_get() API has to be cleaned
by outside.  _edje_entry_cursor_content_get() is calling free() inside of the
function for handle the result using static pointer. But, the caller of
_edje_entry_cursor_content_get() is already handling the result using free().
It can cause double free problem.

The bigger issue is in elementary. See elm_entry_cursor_content_get() API's
document. The document advice developers to free the result when it is done.

@fix

Test Plan: N/A

Reviewers: tasn, raster, woohyun

Subscribers: cedric

Differential Revision: https://phab.enlightenment.org/D2991