hw/virtio/virtio-pci: Remove VIRTIO_PCI_FLAG_DISABLE_PCIE definition

hw/virtio/virtio-pci: Remove VIRTIO_PCI_FLAG_DISABLE_PCIE definition

VIRTIO_PCI_FLAG_DISABLE_PCIE was only used by the hw_compat_2_4[]
array, via the 'x-disable-pcie=false' property. We removed all
machines using that array, lets remove all the code around
VIRTIO_PCI_FLAG_DISABLE_PCIE (see commit 9a4c0e220d8 for similar
VIRTIO_PCI_FLAG_* enum removal).

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <20250512083948.39294-9-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>