adbd: Remove check for set_supplementary_gids.

With https://android-review.googlesource.com/#/c/195400, Minijail will
check for this failure so there's no need to do it here, which allows
to simplify the code.

Bug: 26099611
Change-Id: I7c876fdcab874ed403f82bdd5a4048c0f1e5db58
1 file changed