Add "GTK" prefix to wxChoice::{Dis,En}ableEvents() methods in wxGTK.

Add "GTK" prefix to wxChoice::{Dis,En}ableEvents() methods in wxGTK.

This is more than a cosmetic change: adding "GTK" prefix in wxComboBox and not
doing it in wxChoice in r64436 broke the event generation for wxComboBox as it
didn't override wxChoice methods any longer but defined its own (useless) ones.

Using the same name for the methods in both classes notably fixes unexpected
event generation from wxComboBox::SetSelection().

Closes #12568.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65818 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775