[MIPS] ARC: Get rid of mips_machgroup

This has not been any serious user of this ill conceived thing since the
original invention in like '95.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/setup.c

@@ -51,10 +51,8 @@ EXPORT_SYMBOL(PCI_DMA_BUS_IS_PHYS);
  * These are initialized so they are in the .data section
  */
 unsigned long mips_machtype __read_mostly = MACH_UNKNOWN;
-unsigned long mips_machgroup __read_mostly = MACH_GROUP_UNKNOWN;
 
 EXPORT_SYMBOL(mips_machtype);
-EXPORT_SYMBOL(mips_machgroup);
 
 struct boot_mem_map boot_mem_map;