ice: drop dead code in ice_receive_skb()

napi_gro_receive() can never return GRO_DROP

GRO_DROP can only be returned from napi_gro_frags()
which is the other NAPI GRO entry point.

Followup patch will remove GRO_DROP, because drivers
are not supposed to call napi_gro_frags() if prior
napi_get_frags() has failed.

Note that I have left the gro_dropped variable. I leave to ice
maintainers the decision to further remove it from ethtool -S results.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>