bug#24899: 25.1; x-hide-tip always returns nil with USE_GTK

[martin rudalics]

> Calling `x-hide-tip` always returns nil (it is documented to
> return t when the tooltip is active). I noticed this after
> recently compiling with gtk3. I was using `x-hide-tip` in
> a toggling function that stopped toggling. As an example
> of what currently doesn't work:
>
> (defun toggle-tip ()
>     (interactive)
>     (or (x-hide-tip)
>       (pos-tip-show "hi")))

This should work with Emacs 26 so I'm closing this bug.

Thanks, martin