vgaarb: Drop obsolete #ifndef

Commit 20cde694027e ("x86, ia64: Move EFI_FB vga_default_device()
initialization to pci_vga_fixup()") moved boot video device detection from
efifb to x86 and ia64 pci/fixup.c.

Remove the left-over #ifndef check that will always match since the
corresponding arch-specific define is gone with above patch.

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: Matthew Garrett <matthew.garrett@nebula.com>