arm/xen: remove duplicate arch_gnttab_init() function

This was introduced in commit e306e3be1cbe (Merge tag
'stable/for-linus-3.17-rc0-tag').

Signed-off-by: David Vrabel <[e-mail]>
Acked-by: Stefano Stabellini <[e-mail]>

arch/arm/xen/grant-table.c

···
 {
 	return 0;
 }
-
-int arch_gnttab_init(unsigned long nr_shared, unsigned long nr_status)
-{
-	return 0;
-}