hw/net/vmxnet3: Remove VMXNET3_COMPAT_FLAG_OLD_MSI_OFFSETS definition

hw/net/vmxnet3: Remove VMXNET3_COMPAT_FLAG_OLD_MSI_OFFSETS definition

VMXNET3_COMPAT_FLAG_OLD_MSI_OFFSETS was only used by the
hw_compat_2_5[] array, via the 'x-old-msi-offsets=on' property.
We removed all machines using that array, lets remove all the
code around VMXNET3_COMPAT_FLAG_OLD_MSI_OFFSETS.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <20250512083948.39294-18-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>