Remove Python build parallelism test

The build was successful with '-j4', but it is not worth chasing for the
complication added to the Puppet configuration.  Will keep an eye on
QEMU changelogs for improvements to qemu-user forking/threading.
2 jobs for main in 29 minutes and 32 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
canceled Build cortex-a72-workstation #489
nest

00:29:32

failed Build cortex-a72-workstation #486
nest

02:07:39