Remove note calling Apt a federated cluster

Part of emulab-devel#447
7 jobs for master in 1 minute and 59 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #2425
apt

00:00:39

passed #2426
cloudlab

00:01:38

passed #2427
emulab

00:00:43

passed #2428
phantomnet

00:00:39

passed #2429
powder

00:00:41

 
  Deploy
passed #2430
pages

00:00:20

passed pages:deploy

00:00:01