gtk2 rbgdkcursor.c: drop GTK_CHECK_VERSION(2,8,0)
gtk2 rbgdkwindow.c: drop GTK_CHECK_VERSION(2,8,0)
gtk2 rbgdkdraw.c: drop GTK_CHECK_VERSION(2,8,0)
gtk2 rbgdkscreen.c: drop GTK_CHECK_VERSION(2,8,0)
gtk2 rbgdkdisplay.c: drop GTK_CHECK_VERSION(2,8,0)