OvmfPkg: QemuVideoDxe: eliminate useless Private->HardwareNeedsStarting
    
    Currently, QemuVideoGraphicsOutputQueryMode() reports EFI_NOT_STARTED when
    this boolean field is set.
    
    However, QemuVideoGraphicsOutputQueryMode() is only available to callers
    after the GOP interface has been installed. That in turn implies that the
    following partial call tree has succeeded without errors:
    
      QemuVideoControllerDriverStart()
        QemuVideoGraphicsOutputConstructor()
          QemuVideoGraphicsOutputSetMode(... 0 ...)
            HardwareNeedsStarting = FALSE
        InstallMultipleProtocolInterfaces(... GOP ...)
    
    That is, when QemuVideoGraphicsOutputQueryMode() is reached,
    HardwareNeedsStarting is always FALSE.
    
    Contributed-under: TianoCore Contribution Agreement 1.0
    Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
    Signed-off-by: Laszlo Ersek <lersek@redhat.com>