Tooltips currently don't work well with touchscreens in GTK. They may show up
undesired, don't go away and hinder the interaction.

The GTK setting "gtk-enable-tooltips" to disable is deprecated since 3.10,
unfortunately.

A workaround to get rid of tooltips is setting their opacity to zero.
Additionally set the font size to zero as well to reduce the area that
the now transparent tooltip covers.