hexagon: drop the unused variable zero_page_mask

Hexagon arch does not seem to have subscribed to _HAVE_COLOR_ZERO_PAGE
framework.  Hence zero_page_mask variable is not needed.

Link: http://lkml.kernel.org/r/20180517061105.30447-1-khandual@linux.vnet.ibm.com
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/hexagon/include/asm/pgtable.h

@@ -30,7 +30,6 @@
 
 /* A handy thing to have if one has the RAM. Declared in head.S */
 extern unsigned long empty_zero_page;
-extern unsigned long zero_page_mask;
 
 /*
  * The PTE model described here is that of the Hexagon Virtual Machine,

arch/hexagon/mm/init.c

@@ -39,9 +39,6 @@ unsigned long __phys_offset;	/*  physical kernel offset >> 12  */
 /*  Set as variable to limit PMD copies  */
 int max_kernel_seg = 0x303;
 
-/*  think this should be (page_size-1) the way it's used...*/
-unsigned long zero_page_mask;
-
 /*  indicate pfn's of high memory  */
 unsigned long highstart_pfn, highend_pfn;