Use default message ID lengths

From QXmpp 1.3 this will automatically use UUIDs this way.
3 jobs for uuids in 5 minutes and 37 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #67971
build

00:05:36

passed #67969
clazy

00:05:31

passed #67970
qmllint

00:00:35