README: Drop CONFIG_MPC8349ADS

This option is not used now.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: York Sun <york.sun@nxp.com>

doc/README.mpc83xxads

@@ -50,7 +50,6 @@ Freescale MPC83xx ADS Boards
 
     CONFIG_MPC83xx	    MPC83xx family
     CONFIG_MPC8349	    MPC8349 specific
-    CONFIG_MPC8349ADS	    MPC8349ADS board specific
     CONFIG_TSEC_ENET	    Use on-chip 10/100/1000 ethernet