[ticket/12712] Remove unneeded GROUP BY clause to fix query for mssql

PHPBB3-12712
Merge pull request #2599 from marc1706/ticket/12712

[ticket/12712] Add user_password to GROUP BY clause to fix query for mssql

* marc1706/ticket/12712:
  [ticket/12712] Remove unneeded GROUP BY clause to fix query for mssql