hw/net/e1000: Remove unused E1000_FLAG_MAC flag

hw/net/e1000: Remove unused E1000_FLAG_MAC flag

E1000_FLAG_MAC was only used by the hw_compat_2_4[] array,
via the 'extra_mac_registers=off' property. We removed all
machines using that array, lets remove all the code around
E1000_FLAG_MAC, including the MAC_ACCESS_FLAG_NEEDED enum,
similarly to commit fa4ec9ffda7 ("e1000: remove old
compatibility code").

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>
Message-ID: <20250512083948.39294-7-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>