x86: remove redundant pfn_pmd definition

Impact: cleanup

It's already defined in pgtable.h
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

arch/x86/include/asm/pgtable_64.h

@@ -191,7 +191,6 @@ static inline int pud_large(pud_t pte)
 }
 
 /* PMD  - Level 2 access */
-#define pfn_pmd(nr, prot) (__pmd(((nr) << PAGE_SHIFT) | pgprot_val((prot))))
 #define pmd_pfn(x)  ((pmd_val((x)) & __PHYSICAL_MASK) >> PAGE_SHIFT)
 
 #define pte_to_pgoff(pte) ((pte_val((pte)) & PHYSICAL_PAGE_MASK) >> PAGE_SHIFT)