makefile: remove duplicated unit test execution

Fix an issue in openvswitch utilities automake file that caused the
openvswitch unit tests execute two times.

Change-Id: I133dee0c474d4ab51ee0fe10cfa916efd90a978c
Reviewed-by: Mark D. Gray <mark.d.gray@intel.com>
Reviewed-by: Meghan Halton <meghan.halton@intel.com>
Signed-off-by: Nicolas Pernas Maradei <nicolasx.pernas.maradei@intel.com>