The OAuth administrator group was removed from mediawiki.org. As can be seen at Special:ListGroupRights the group is no longer there but before the group was removed from mediawiki and transfered to Meta-Wiki, several users remained as members of the group: https://www.mediawiki.org/wiki/Special:ListUsers?username=&group=oauthadmin

With oauthadmin not existing on mediawiki.org; this cannot be removed locally so the option is that stewards do so from Meta, or run the emptyUserGroup.php MW core maintenance script to do so.

In either case, this is non-controversial as, like I said, the group and permissions no longer exists on mediawiki so its holders will not loose any ability.