For some reasons wxBookCtrlBase::GetControllerSize() was redefined in several
derived classes even though it did exactly the same thing in all of them.
Leave only the base class version and remove the other ones.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63630 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775