gtk-demo/theming: Don’t mislead about raised class

gtk-demo/theming: Don’t mislead about raised class

This class is not added by any widgets nor themed by Adwaita/HC.
However, it is presented here as if it does something. It doesn’t.

But we changed the 2 buttons with the .raised class to use symbolic
icons, unlike their ‘unraised’ counterparts, which is unnecessarily
confusing and might make people think .raised affects icons somehow.

So, make them use the same icons in all cases; that way, if .raised is
ever made to do anything, 6 years later, what it does will be clear.

https://bugzilla.gnome.org/show_bug.cgi?id=644248