SSD booting slower than rotary HD? You might have a ghost disk reference

I changed to an SSD, re-installed Ubuntu 16.04LTS and my boot times slowed to a crawl. Turned out the installation script had put in an imaginary swap drive in  my /etc/fstab. Systemd then waited for it, for a minute or so while booting. In the logs (which you reach with journalctl on systemd) it looked something like this:

sep 15 23:25:33 hostname NetworkManager[2733]: <info>  [1473974733.3738] WWAN hardware radio set enabled
sep 15 23:26:09 hostname systemd[1]: Starting Stop ureadahead data collection...

Or like this:

sep 16 00:54:40 hostname kernel: nouveau 0000:01:00.0: DRM: suspending kernel object tree...
sep 16 00:56:03 hostname systemd[1]: dev-disk-by\x2duuid-7553704f\x2d1ffd\x2d490b\x2db12b\x2d5174b3464643.device: Job dev-disk-by\x2duuid-7553704f\x2d1ffd\x2d490b\x2db12b
sep 16 00:56:03 hostname systemd[1]: Timed out waiting for device dev-disk-by\x2duuid-7553704f\x2d1ffd\x2d490b\x2db12b\x2d5174b3464643.device.

In the second one I could use gparted to find out what disk ids were and weren't present on my system. The comments in fstab indicated the wrong one, that is the existing swap was preceded by the comment:

# swap was on /dev/sdb2 during installation

While that one is on /dev/sda5 actually, and the non-existing one was marked up with:

# swap was on /dev/sda5 during installation