syscalls: Old setgroups(2)/getgroups(2): Remove superfluous STD type

An examination of the scripts under 'sys/tools/syscalls' indicates that
keeping STD as a type in the presence of COMPATxx does not make any
difference, and regenerating system call files with STD removed does
indeed not show any difference. Moreover, this practice is inconsistent
with the rest of the file.

Thus, remove the superfluous STD type for the two above-mentioned system
calls. While here, re-order the remaining types for getgroups() to be
consistent with other such occurences (COMPATxx before CAPENABLED).

Reviewed by: kevans, emaste
MFC after: 5 days
MFC to: stable/15
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52499

(cherry picked from commit 696cfb27ca4e60ebd49c45355a8a9c4945f84f98)