[EFL][WK2] Update text checker documentation.
https://bugs.webkit.org/show_bug.cgi?id=117828

Reviewed by Christophe Dumez.

* UIProcess/API/efl/ewk_text_checker.h:
The client is not responsible for destroying the memory.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@151775 268f45cc-cd09-0410-ab3c-d52691b4dbfc