Revert "Fix off by 1 error in wxGenericListCtrl::HitTest()."

Revert r73563, this breaks the selection in the control apparently.

See #15063.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73596 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775