gtk2 rbgdkdragcontext.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtktreeview.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkcellrenderercombo.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkentrycompletion.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkdialog.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtkcombobox.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtktextbuffer.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgdkwindow.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgtktextview.c: drop GTK_CHECK_VERSION(2,6,0)
gtk2 rbgdkevent.c: drop GTK_CHECK_VERSION(2,6,0)