content_box is useless and also it make recursive calcuation by
adding win resize object which was already set by parent box.
this patch removing useless content_box object and make Check Cursor
works properly as it intended.
Slider can have two indicators if enabled and user can select
range values.
phab: https://phab.enlightenment.org/D3822
Test Plan: elementary_test -to slider
@feature
Change-Id: If4ca74de6f5a94531ebd21750d52704b2b02afee