x86, vdso, xen: Remove stray reference to FIX_VDSO

Checkin

    b0b49f26 x86, vdso: Remove compat vdso support

... removed the VDSO from the fixmap, and thus FIX_VDSO; remove a
stray reference in Xen.

Found by Fengguang Wu's test robot.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Link: http://lkml.kernel.org/r/4bb4690899106eb11430b1186d5cc66ca9d1660c.1394751608.git.luto@amacapital.netSigned-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/xen/mmu.c

@@ -2058,7 +2058,6 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
 	case FIX_RO_IDT:
 #ifdef CONFIG_X86_32
 	case FIX_WP_TEST:
-	case FIX_VDSO:
 # ifdef CONFIG_HIGHMEM
 	case FIX_KMAP_BEGIN ... FIX_KMAP_END:
 # endif