e1000e: remove unnecessary internal msi state flag

e1000e: remove unnecessary internal msi state flag

Internal big flag E1000E_USE_MSI is unnecessary, also is the helper
function: e1000e_init_msi(), e1000e_cleanup_msi(), so, remove them all.

cc: Dmitry Fleytman <dmitry@daynix.com>
cc: Jason Wang <jasowang@redhat.com>
cc: Markus Armbruster <armbru@redhat.com>
cc: Marcel Apfelbaum <marcel@redhat.com>
cc: Michael S. Tsirkin <mst@redhat.com>

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>