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/msw/checkbox.cpp

@@ -174,9 +174,7 @@ wxSize wxCheckBox::DoGetBestClientSize() const
         hCheckbox = s_checkSize;
     }
 
-    wxSize best(wCheckbox, hCheckbox);
-    CacheBestSize(best);
-    return best;
+    return wxSize(wCheckbox, hCheckbox);
 }
 
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