spec: remove duplicate entry for BuildRequires

Change-Id: I23402f4a49f1e606323da1e4e009450ee440d136
BuildRequires: python-ethtool appears twice.
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27060
Reviewed-by: Dan Kenigsberg <danken@redhat.com>