Don't call CacheBestSize() from DoGetBestSize() implementations

This is unnecessary, wxWindow::GetBestSize() already does this, so calling it
from DoGetBestSize() called by it too is just useless.

src/gtk/gauge.cpp

@@ -77,7 +77,6 @@ wxSize wxGauge::DoGetBestSize() const
         best = wxSize(28, 100);
     else
         best = wxSize(100, 28);
-    CacheBestSize(best);
     return best;
 }