Remove Palm OS port.

The platform targeted by this port doesn't exist any more and the port never
achieved really working state so remove the code to avoid having to maintain
it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70345 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/radiobox.h

@@ -19,9 +19,6 @@
     @style{wxRA_SPECIFY_COLS}
            The major dimension parameter refers to the maximum number of
            columns.
-    @style{wxRA_USE_CHECKBOX}
-           Use of the checkbox controls instead of radio buttons (currently
-           supported only on PalmOS)
     @endStyleTable
 
     @beginEventEmissionTable{wxCommandEvent}