Revert "API: Fix list=allusers with multiple values for augroup"

Causing a large load spike on enwiki api db slaves

This reverts commit aa5800519f301cbafa835ef3ee95c7b3f24050b4.

Change-Id: Ied559c4e701bb644b354af4e158b84537dde94e9
Merge "Revert "API: Fix list=allusers with multiple values for augroup"" into wmf/1.25wmf1