mainboard: Remove last_boot NVRAM option

The last_boot NVRAM option was deprecated and removed in
commit 3bfd7cc6.  Remove the last_boot option from all
affected mainboards to eliminate user confusion.

Change-Id: I7e201b9cf21dfe5dda156785bad078524098626d
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: http://review.coreboot.org/12316
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins)
diff --git a/src/mainboard/pcengines/apu1/cmos.layout b/src/mainboard/pcengines/apu1/cmos.layout
index 0cf145f..e0501f6 100644
--- a/src/mainboard/pcengines/apu1/cmos.layout
+++ b/src/mainboard/pcengines/apu1/cmos.layout
@@ -3,7 +3,6 @@
 # <start-bit> <bit-length> <config> <config-id> <parameter-name>
 0             384          r        0           reserved_memory
 384           4            r        0           reboot_bits
-388           1            e        2           last_boot
 # leave 3 bits to make checksummed area start byte-aligned
 392           1            e        2           boot_option
 393           1            e        1           multi_core
@@ -18,7 +17,7 @@
 ## for multi_core
 1             0        Enable
 1             1        Disable
-## for last_boot, boot_option
+## for boot_option
 2             0        Fallback
 2             1        Normal
 ## for baud_rate