xen/x86: there's no highmem anymore in PV mode

Considerations for it are a leftover from when 32-bit was still
supported.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/ba6e0779-18f4-ae64-b216-73205b4eec3c@suse.com
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/x86/xen/setup.c

@@ -306,10 +306,6 @@ static void __init xen_update_mem_tables(unsigned long pfn, unsigned long mfn)
 		BUG();
 	}
 
-	/* Update kernel mapping, but not for highmem. */
-	if (pfn >= PFN_UP(__pa(high_memory - 1)))
-		return;
-
 	if (HYPERVISOR_update_va_mapping((unsigned long)__va(pfn << PAGE_SHIFT),
 					 mfn_pte(mfn, PAGE_KERNEL), 0)) {
 		WARN(1, "Failed to update kernel mapping for mfn=%ld pfn=%ld\n",