ArmVirtPkg: remove now unused PciHostBridgeDxe
    
    This code is now no longer used, so remove it.
    
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Reviewed-by: Laszlo Ersek <lersek@redhat.com>
    Ref: https://tianocore.acgmultimedia.com/show_bug.cgi?id=65