m68knommu: remove no longer used rom_length from Palm/Pilot start up code

Compiling for the m68knommu/68328 Palm/Pilot target you get:

  LD      vmlinux
arch/m68k/platform/68328/head.o: In function `L3':
(.text+0x170): undefined reference to `rom_length'

"rom_length" is not used any longer by any of the m68knommu code.
So remove it from here too.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>

arch/m68k/platform/68328/head-pilot.S

@@ -173,9 +173,6 @@ L3:
 	moveq	#79, %d7
 	movel	%d0, _ramend
 
-	movel	%a3, %d0
-	movel	%d0, rom_length
-
 	pea	0
 	pea	env
 	pea	%sp@(4)