nk_widget_fitting() is a useless wrapper around nk_widget()

[rswinkle]

So I randomly stumbled across this.

Thanks to this fix and the subsequent fix nk_widget_fitting() has been useless since 2020.

It is an internal function and used only 3 times in nuklear_contextual.c. At the very least we should just change those calls to nk_widget() but I think we should just remove it entirely. I'd be surprised if anyone anywhere is using it in user code if there ever was even when it did something.