boot0: Drop the BOOT_BOOT0_ORG option.

This shouldn't be an option (and I added it in the first place back in
4ae4202 and
83f4b92).  However, unlike the other
knobs I added back then, this really shouldn't be a knob since it is
hardcoded in the source.

stand/i386/boot0/Makefile

@@ -39,10 +39,8 @@ BOOT_BOOT0_TICKS?=	0xb6
 # The BIOS loads boot0 to the hardcoded address 0x7c00.  boot0 copies
 # itself to this alternate base address before continuing execution so
 # that next level boot blocks can be loaded at the 0x7c00 address they
-# expect.  Don't change this unless you are glutton for punishment
-# (and fix ORIGIN in the source to match).
-BOOT_BOOT0_ORG?=	0x600
-ORG=${BOOT_BOOT0_ORG}
+# expect.
+ORG=	0x600
 
 # Comm settings for boot0sio.
 #