Fix text updated event generation in wxGTK wxComboBox.

Fix text updated event generation in wxGTK wxComboBox.

The changes (cosmetic renaming, no less) in r64436 broke unit tests checking
for wxComboBox event generation because the extra text updated events were not
suppressed correctly any longer because wrong {Enable,Disable}Events() were
called instead of the correct GTK{Enable,Disable}Events().

Fix and slightly improve the code by disabling the events in overridden
EnableTextChangedEvents() itself and reuse its code from GTK-specific event
enabling functions.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64916 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775