[ARM] Fix ARM "make help" output

Remove "initrd" target from help - it isn't a user target.

arch/arm/Makefile

@@ -182,7 +182,6 @@ define archhelp
   echo  '* zImage        - Compressed kernel image (arch/$(ARCH)/boot/zImage)'
   echo  '  Image         - Uncompressed kernel image (arch/$(ARCH)/boot/Image)'
   echo  '  bootpImage    - Combined zImage and initial RAM disk' 
-  echo  '  initrd        - Create an initial image'
   echo  '  install       - Install uncompressed kernel'
   echo  '  zinstall      - Install compressed kernel'
   echo  '                  Install using (your) ~/bin/installkernel or'