The IDs of packages are unique, so there is no need to group search
results by package ID.

Note that the GROUP BY statement in question was introduced in commit
3447dfcb

 (Support versioned RPC queries, 2014-04-28) for no apparent
reason and could even lead to errors in various DBMS.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>