wxDialogBase only has one ctor, so just do initialization in ctor instead of Init()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74699 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
remove redundant initialization of base class member variables

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74700 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775