[dts] [PATCH V1] tests/flexible_rxd: remove one unsupported case

[Tu, Lijuan]

> Confirmed with developer,only type=0x8100 needs to be supported in single vlan
> mode,
> 
> other type values do not need to be verified, so remove the type=0x88A8 case
> from
> 
> test suite and plan.
> 
> Signed-off-by: sunqin <qinx.sun at intel.com>

Applied.