MIPS: Remove unused HIGHMEM_DEBUG macro

We have a HIGHMEM_DEBUG macro defined in asm/highmem.h with a comment
stating that it should be removed for production, and no users... Kill
it.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14523/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/highmem.h

@@ -25,9 +25,6 @@
 #include <asm/cpu-features.h>
 #include <asm/kmap_types.h>
 
-/* undef for production */
-#define HIGHMEM_DEBUG 1
-
 /* declarations for highmem.c */
 extern unsigned long highstart_pfn, highend_pfn;